World 4 (Dr. Mario World)

World 4 is a haunted forest world in Dr. Mario World. It is available since the initial version of this game.

When an area is cleared, Boos and Peepas appear. The viruses featured in the regular stages are red, green and light-blue.

Stage names in bold red text are labelled as hard stages in the game.

Area 1

Image	Stage	Best Doctors	Overview
	Stage 121	Dr. Yoshi Dr. Toad	This stage introduces dust viruses, which are viruses that are hidden in dust until a capsule lands next to it or an adjacent object is destroyed. If a valid match is made even though viruses in dust are not revealed, it will still be eliminated. The objective of this stage is to eliminate all viruses. This stage is shaped like a ghost, with exploders shaping its eyes. Some Brick Blocks are present in this stage.
	Stage 122	Dr. Lakitu Dr. Luigi	The objective of this stage is to eliminate all viruses. In this stage, there is a path of viruses interspersed with dust viruses. A red lock block is located between two Empty Blocks, which will unlock red cages containing viruses and a green lock block. The green cages contain viruses and Brick Blocks.
	Stage 123	Dr. Ludwig Dr. Waluigi	The objective of this stage is to eliminate all viruses. In this stage, viruses are lined up along the sides, top and a row near the bottom, with most of them being half-frozen. In the middle, dust viruses are found above Empty Blocks.
	Stage 124	Dr. Fire Rosalina Dr. Toad	The objective of this stage is to eliminate all viruses. In this stage, cages are lined up diagonally, one line containing viruses and another containing floatie viruses. The corresponding lock blocks are found on the outside of the diagonal line with Brick Blocks.
	Stage 125	Dr. Luma Dr. Fire Mario	The objective of this stage is to collect all virus coins. In this stage, there are two groups with two columns each has viruses each with four virus coins each, and in each group, the ones in the middle rows are half-frozen. In the middle column, there are fully-frozen viruses with exploders, and each virus cover a virus coin. Two columns with Brick Blocks and Empty Blocks are located between the middle column. The capsule amount is increased from 32 to 37 since version 1.3.5. Besides that, this stage is otherwise the same.
	Stage 126	Dr. Toadette Dr. Yoshi	The objective of this stage is to eliminate all viruses. In this stage, a shell is in the middle of the stage where it is in the same row as two lock blocks and two floatie viruses. The cages form both a "v" and an upside-down "v". All the Brick Blocks contain hidden viruses.
	Stage 127	Dr. Waluigi Dr. Toad	The objective of this stage is to eliminate all viruses. This stage is shaped like a spade that is mostly formed by dust viruses and a half-frozen lock block in the middle that corresponds to four caged viruses in the corners.
	Stage 128	Dr. Baby Rosalina Dr. Fire Mario	The objective of this stage is to eliminate all viruses. In this stage, there are two symmetrical groups of viruses that are in cages with the middle ones being free. There are viruses inside bubbles surrounded by Brick Blocks on the leftmost and rightmost columns, and a shell in the middle column in the top row. The Brick Blocks in the second and eighth columns contain lock blocks in the second row and hidden viruses in the other rows. The capsule amount is increased from 40 to 45 since version 1.3.5. Besides that, this stage is otherwise the same.
	Stage 129	Dr. Mario Dr. Waluigi	The objective of this stage is to eliminate all viruses. In this stage, dust viruses are in the leftmost and rightmost columns, along with one in the middle column in the topmost row. Hidden viruses are found in Brick Blocks, and some viruses are half-frozen and fully-frozen.
	Stage 130	Dr. Yoshi Dr. Wendy	The objective of this stage is to collect all coins from Coin Blocks. This stage is shaped like a flower. Viruses in cages are found next to Brick Blocks (all containing coins), with the corresponding lock block near the bottom row. An exploder is in the middle of the Brick Blocks.
	Stage 131	Dr. Fire Peach Dr. Fire Mario	The objective of this stage is to eliminate all viruses. This stage is shaped like a ghost flipped 90 degrees counter-clockwise. Three floatie viruses are found in the sixth row and three dust viruses are found in the fifth to seventh rows each found in one row. Half-frozen viruses can be found in the first three columns. Hidden viruses are found in the Brick Blocks in the seventh column except for the one in the middle.
	Stage 132	Dr. Toadette Dr. Baby Rosalina	The objective of this stage is to eliminate all viruses. This stage is shaped like a clock pointing to 8 o' clock, with the hands formed by dust viruses all containing floatie viruses.
	Stage 133	Dr. Fire Peach Dr. Peach	The objective of this stage is to eliminate all viruses. In this stage, viruses (normal, caged and half-frozen) and a few dust viruses are found in the odd-numbered columns, with floatie viruses inside bubbles found in the even-numbered columns. The Brick Block contains a hidden lock block, and the lock block in the rightmost column is fully-frozen. The lock block in the middle column is locked behind a cage.
	Stage 134	Dr. Fire Rosalina Dr. Fire Peach	The objective of this stage is to eliminate all viruses. In this stage, there are viruses in bubbles and hidden viruses in all the Brick Blocks. Exploders are found in the middle column and the topmost row, and a shell is found in the topmost row at the middle column.
	Stage 135	Dr. Wario Dr. Wendy	The objective of this stage is to collect all coins from Coin Blocks. In this stage, the floatie viruses are surrounded by viruses in a "+" pattern, except for the bottom-most row ones where the bottom is open. All Brick Blocks in this stage contain coins.
	Stage 136	Dr. Waluigi Dr. Yoshi	The objective of this stage is to eliminate all viruses. In this stage, there are three groups of viruses in mirrored "L" patterns containing dust viruses and viruses inside bubbles, and a group of fully-frozen four viruses in the top-left corner. At each group's bottom-right corner, a mirrored "L" pattern of Brick Blocks separate them.
	Stage 137	Dr. Luigi Dr. Toad	The objective of this stage is to eliminate all viruses. This stage is shaped like a percentage (%) symbol. All Brick Blocks contain hidden viruses, an in the middle are lock blocks that will unlock the circle portions of the percentage symbol. Some viruses are fully-frozen. The capsule amount is increased from 39 to 46 since version 1.3.5. Besides that, this stage is otherwise the same.
	Stage 138	Dr. Bowser Dr. Waluigi	The objective of this stage is to eliminate all viruses. In this stage, the top two rows has columns of dust viruses between Brick Blocks, while the bottom two rows contain viruses inside bubbles initially between dust viruses. Between them are three rows of five viruses (two of them half-frozen) between Empty Blocks, arranged in a cascade fashion.
	Stage 139	Dr. Waluigi Dr. Baby Mario	The objective of this stage is to eliminate all viruses. In this stage, there is an outer ring of Brick Blocks where dust viruses are found in the corners and hidden viruses are found in the center of each of the sides. There is another ring containing Brick Blocks and Empty Blocks, in which viruses are also found in the center of each side, two of them hidden in Brick Blocks. Between the two rings are floatie viruses in the corners and dust viruses on the center of each side, and on the inside of the inner ring, there are more dust viruses.
	Stage 140	Dr. Koopa Troopa Dr. Bowser	The last stage of the first area, the objective of this stage is to eliminate all viruses. In the beginning of this stage, four dust viruses each containing floatie viruses are found, along with a group of five viruses above a row of Brick Blocks. Five more viruses are surrounded by Brick Blocks, and the Brick Blocks initially found in the third row contain hidden viruses. After the stage scrolled up far enough, there are viruses in cages with hidden viruses in Brick Blocks found to the left and below of the group. The lock block is hidden in the Brick Block in the third row at the seventh column after the stage scrolled up all the way. This stage will scroll for one line each time enough objects are cleared, and will stop after 5 lines are introduced. When cleared, the rest of the first area in the world map gets cleared of viruses. Players also obtain 500 coins upon completing this stage. Prior to version 1.3.5, the stage layout was different. The following changes were made: Two viruses are added in the second row from top after the stage scrolled up all the way, in the rightmost two columns.

Area 2

Image	Stage	Best Doctors	Overview
	Stage 141	Dr. Bowser Dr. Yoshi	The objective of this stage is to eliminate all viruses. In this stage, green cages are arranged in a spiral, with its corresponding lock block between one of the Brick Blocks between the spiral. Every Brick Block except for the ones in the first row and the eighth row contains hidden viruses.
	Stage 142	Dr. Fire Mario Dr. Luigi	The objective of this stage is to eliminiate all viruses. In this stage, a column of shells are in the same row as Brick Blocks, along with an exploder below one of the shells. The column of Brick Blocks next to the shells contain hidden exploders, and after all the Brick Blocks are destroyed, some floatie viruses and a formation of viruses in the shape of a moon are revealed. Above and below the formation, there are dust viruses, floatie viruses covered in dust and Empty Blocks covered in dust.
	Stage 143	Dr. Yoshi Dr. Fire Mario	The objective of this stage is to eliminate all viruses. This stage is shaped like a cross, where the viruses are locked behind cages. The lock blocks which are fully-frozen are found near the corners, and there are half-frozen floatie viruses near the other corners. The Brick Blocks in the sixth row contain hidden viruses. Prior to version 1.3.5, the stage layout was different. The following changes were made: Capsule amount is increased from 40 to 43. Floatie viruses are half-frozen instead of fully-frozen.
	Stage 144	Dr. Baby Luigi Dr. Waluigi	The objective of this stage is to eliminate all viruses. In this stage, there are some viruses that are fully-frozen and one that is half-frozen, along with some dust viruses. Exploders are located in a "+" pattern near the bottom.
	Stage 145	Dr. Baby Peach Dr. Diddy Kong	This stage introduces caged coins, which are purple coins that are locked behind cages. Caged coins are unlocked in a sequence of groups, which require the currently-unlocked purple coins are collected. The objective of this stage is to collect all purple coins. Most of the purple coins are found between viruses, and one of them is between half-frozen Brick Blocks. Purple coins are unlocked in the following sequence: The coins in the eighth row. The coins in the second column. The coins in the eighth column. The coins in the second row. The coin in the middle surrounded by the half-frozen Brick Blocks.
	Stage 146	Dr. Lakitu Dr. Daisy	The objective of this stage is to eliminate all viruses. In this stage, five groups of Brick Blocks are inside cages, with the groups placed in a cross pattern. Between the groups are groups of viruses which include floatie viruses arranged in two rows, with two of the groups containing one lock block each. The capsule amount is increased from 38 to 40 since version 1.3.5. Besides that, this stage is otherwise the same.
	Stage 147	Dr. Kamek Dr. Fire Peach	The objective of this stage is to eliminate all viruses. In this stage, there is a ring of viruses inside bubbles surrounding Brick Blocks with a dust virus in the middle, and that ring is surrounded by Empty Blocks below and Brick Blocks on other sides, with two spaces open. On the outside, there are more viruses and dust viruses. The Brick Blocks to the top-left, bottom-left and bottom-right of the dust virus surrounded by Brick Blocks contain hidden viruses.
	Stage 148	Dr. Koopa Troopa Dr. Fire Peach	The objective of this stage is to eliminiate all viruses. In this stage, there is a path of Brick Blocks swerving around columns of Empty Blocks, with a few viruses below the Brick Blocks. Hidden viruses are found behind the following Brick Blocks: Bottom five Brick Blocks in the first row. Second, fourth and sixth of Brick Blocks in the third and middle columns. Brick Blocks in the fourth, sixth and eighth columns. Third, fourth, sixth and eighth Brick Blocks in the seventh column. Third, sixth, seventh and eighth Brick Blocks in the rightmost column.
	Stage 149	Dr. Bowser Dr. Baby Peach	The objective of this stage is to eliminate all viruses. In this stage, viruses form a diamond line, with the corners full-frozen except the bottom. They are surrounded by Empty Blocks except for the bottom, and Brick Blocks fill the outside of the Empty Blocks. The capsule amount is increased from 45 to 50 since version 1.3.5. Besides that, this stage is otherwise the same.
	Stage 150	Dr. Baby Mario Dr. Mario	The objective of this stage is to collect all purple coins. In this stage, the coins and viruses are in a symmetrical pattern, where each side has coins, Brick Blocks, Empty Blocks and viruses (regular, inside bubbles, fully-frozen and dust viruses) are on each side. Purple coins are unlocked in the following sequence: The coins in the ninth row. The coin hidden in dust in the middle column. The group of initially half-frozen coins on the left in the seventh row. The group of initially half-frozen coins on the right in the seventh row. The group of coins on the left in the second and third rows. The group of coins on the right in the second and third rows. Prior to version 1.3.5, the stage layout was different. The following changes were made: Capsule amount is increased from 30 to 33. Two Empty Blocks in the fifth row are changed to Brick Blocks.
	Stage 151	Dr. Luma Dr. Kamek	The objective of this stage is to eliminate all viruses. This stage is shaped like an "S" and is formed by Brick Blocks all containing hidden viruses, exploders and viruses. The red viruses are fully-frozen while the green viruses are half-frozen.
	Stage 152	Dr. Baby Mario Dr. Fire Mario	The objective of this stage is to eliminate all viruses. In this stage, two groups of viruses in the shape of an "H" are found in the middle three columns, in which the ones in the middle column are dust viruses and the viruses closer to the middle row are fully-frozen. Additional viruses are found in the second and eighth columns surrounded by Brick Blocks and Empty Blocks where the bottom ones are inside bubbles while the top ones are not.
	Stage 153	Dr. Luma Dr. Fire Peach	The objective of this stage is to eliminate all viruses. This stage is shaped like an "O" where the viruses on the leftmost and rightmost columns are half-frozen, and there are a row of Brick Blocks in the topmost row. In the middle of the stage is a skill charger.
	Stage 154	Dr. Luigi Dr. Peach	The objective of this stage is to eliminiate all viruses. In this stage, cages are lined up vertically in broken lines parted by dust viruses containing floatie viruses and exploders. A lock block is found in the eighth column, and another lock block is found inside a cage in the second column.
	Stage 155	Dr. Daisy Dr. Mario	The objective of this stage is to collect all purple coins. In this stage, rows containing purple coins are between rows containing viruses in cages. On the leftmost and rightmost columns, there are fully-frozen lock blocks and a virus. Purple coins are unlocked in the following sequence: The coins in the eighth row. The coins in the sixth row. The coins in the fourth row. The coins in the second row. The capsule amount is increased from 28 to 33 since version 1.3.5. Besides that, this stage is otherwise the same.
	Stage 156	Dr. Baby Rosalina Dr. Baby Peach	The objective of this stage is to eliminate all viruses. This stage is shaped like a butterfly. In this stage, there is a shell in the same row as the lock blocks, which will unlock the cages in the rows above them. Besides that, there are viruses inside bubbles below that row and a couple of dust viruses in the third row.
	Stage 157	Dr. Donkey Kong Dr. Baby Rosalina	The objective of this stage is to eliminate all viruses. In this stage, the corners contain two groups of viruses locked behind cages and another two groups that are half-frozen. A lock block and eight viruses are partially surrounded by Brick Blocks in the middle.
	Stage 158	Dr. Daisy Dr. Fire Mario	The objective of this stage is to eliminate all viruses. In this stage, there are three rings of cages that locked Brick Blocks, Empty Blocks and in the middle ring of cages, a few viruses. In the middle of the ring of cages, there are viruses inside bubbles on the left and right rings, while viruses and a lock block is in the middle ring. Two other lock blocks are half-frozen among the like-colored half-frozen viruses.
	Stage 159	Dr. Luigi Dr. Toad	The objective of this stage is to eliminate all viruses. In this stage, there are two columns of viruses behind cages, some with floatie viruses. The lock block is fully-frozen and is found among viruses in a formation of a hat. Additional viruses are hidden in the Brick Blocks in the fourth and sixth columns, except the ones in the topmost row. Prior to version 1.2.0, the stage layout was different. The following changes were made: Capsule amount is increased from 40 to 46. The viruses in the eighth row are no longer hidden in Brick Blocks.
	Stage 160	Dr. Toad Dr. Bowser Jr.	The final stage is a scrolling stage that requires all viruses to be eliminated. In this beginning, there are three columns of three viruses in the middle, along with a shell in the same row as the one in the middle. The other viruses are between Brick Blocks, and as the stage scrolls, half-frozen viruses and viruses inside bubbles appear in addition to the regular viruses. This stage will scroll for one line each time enough objects are cleared, and will stop after 10 lines are introduced. Once it is cleared, the remaining area of the stage map gets cleared of viruses, and players can access World 5. Upon completion, players earn a free Staff Ticket that lets them unlock either a new doctor, a new assistant, or leveling up an existing doctor or assistant. Prior to version 1.2.0, the stage layout was different. The following changes were made: Capsule amount is increased from 48 to 55. In the beginning before the stage scrolls, the fifth row has a shell in the rightmost column instead of a Brick Block.

Challenge stages

Image	Stage	Best Doctors	Overview
	Stage 4A	Dr. Diddy Kong Dr. Baby Daisy	Within a 52 second time limit, players need to eliminate all viruses and collect all purple coins. In this stage, there are four rows of purple coins (both caged and uncaged) with Brick Blocks between them, along with rows of viruses between those rows where they are between the Brick Blocks. Purple coins are unlocked in the following sequence: The coins in the eighth row. The coins in the sixth row. The coins in the fourth row. The coins in the second row. Starting from version 1.2.0, completing this stage awards the player 500 coins.
	Stage 4B	Dr. Kamek Dr. Fire Mario	Within a 105 second time limit, players need to eliminate all viruses. In this stage, two rows of viruses are locked behind cages, and in between the rows, the corresponding lock blocks are found among dust containing floatie viruses. Starting from version 1.2.0, completing this stage awards the player 500 coins.
	Stage 4C	Dr. Wario Dr. Wendy	Within a 75 second time limit, players need to eliminate all viruses. This stage is shaped like the letter "Z" where one group consists of regular viruses, one group consists of viruses inside bubbles and another group are Brick Blocks. Among the Brick Blocks, one diagonal line of them are fully-frozen, another consists of two hidden viruses as well as six floatie viruses and another line do not contain anything. Completing this stage awards the player 1000 coins and a Staff Ticket (3 Hearts prior to version 1.2.0).

Special Stage

Image	Stage	Best Doctors	Overview
	Special Stage	Dr. Yoshi Dr. Wario	The objective of this stage is to eliminate all viruses. In the beginning, there are five columns of cages with Empty Blocks in between containing floatie viruses in the middle column, one lock block in the rightmost column and viruses in the other spots. The bottom-most row of Brick Blocks contain hidden viruses, while the Brick Blocks in the row above the cages do not. Additional floatie viruses appear when the stage scrolls up once, and in the three rows after that, more viruses and Brick Blocks each containing hidden viruses appear. This stage will scroll for one line each time enough objects are cleared, and will stop after 5 lines are introduced. Completing this stage awards the player 1000 coins and Dr. Luigi.

Stage layouts in previous versions

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  Stage 140 prior to version 1.3.5. Note the amount of viruses required to be eliminated.

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  Stage 143 prior to version 1.3.5

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  Stage 150 prior to version 1.3.5

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  Stage 159 prior to version 1.2.0

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  Stage 160 prior to version 1.2.0