Thunderhand
Thunderhand is a move used by Luigi during the events of Mario & Luigi: Superstar Saga. It is also the brother move of the Firebrand. He is taught this by the Thunder God in the Thunder Palace. It is even further advanced after Merri teaches him how to use it along with Mario.
Thunderhand can power Lightning Orbs and defeat thunder-prone enemies. It was the only way to defeat the Piranha Plants that cover the runway on the Beanbean International Airport. In battle it proves useful against certain enemies. They can also use Thunder Bros. after the Jellyfish Sisters teach Luigi the advanced method. After the advanced method is taught, Luigi can tickle Mario causing them to "stick together" and move faster. This can be used to pass through slow-moving spiked barrels and activate Boo Statues.
Besides Luigi, Merri and the Thunder God, it can be said that Cackletta also knows it. One of Cackletta's moves during the final battle, when Cackletta snaps her right fingers, she will create a ball of thunder. Because the Thunder God tells Luigi that no one has visited the Thunder Temple in 3000 years, Cackletta is possibly at least that old. However, this may also be just a normal power of Cackletta, just like shooting energy balls or creating a fake Fawful.
This power has not been mentioned since this game, although in Mario Strikers Charged, Luigi's Mega Strike involves him using electricity. In Super Paper Mario, Mr. L referred to himself by the nickname The Green Thunder. However, he may have lost it for unknown reasons.
