Smelter

Smelter is a member of the Smithy Gang and is the source of Smithy's minions; he is found during the events of Super Mario RPG: Legend of the Seven Stars. Smelter produces the hot liquid metal used by Smithy to create his robotic armies. Using his sledgehammer, Smithy pounds the metal into various monstrosities, including Jabbits and the Machine Mades, which are then sent to the assembly lines before being ordered to attack Mushroom World.

During Mario's final battle with Smithy, Smelter produces an unending supply of Shypers, the most powerful version of the Shyster. These Shypers wield some of the strongest attacks in the game. As such, Mario and company should focus their attacks on Smelter, before concentrating on Smithy. With Smelter removed from the picture, the fight becomes much easier for Mario and his allies.

Trivia

 * Most likely by coincidence, Smelter bears a strong resemblance to Birdo.