Croco

Croco is a purple crocodile thief from Super Mario RPG: Legend of the Seven Stars.

Mario first sees Croco being chased by Mallow. When Croco escapes, Mallow starts to cry. Mario comes up to him and Mallow tells him that Croco stole his grandpa's Frog Coin. Mario agrees to get the Frog Coin back for Mallow.

After chasing Croco, Mario and Mallow battle him and defeat him. Croco gives back the Frog Coin, but he tells Mario that this isn't the last time they'll see him.

And he's telling the truth - When Mario, Mallow and Geno use a spring in the Moleville Mines that takes them up to the ceiling, Mario faints and Croco steals all Mario's coins! After chasing Croco again, Mario, Mallow and Geno battle him. Half way through the battle, Croco steals all of Mario's items, but he gives the coins and items back at the end of the fight.

Croco doesn't appear again until near the end of the game in Bowser's Keep. This time he doesn't battle you - instead, he sells you items for some reason. He also happens to be near a treasure block that contains infinite coins made by Magikoopa, so you can buy anything you need.