Mega Koopa

From Paper Mario Wiki

Mega Koopa is a Koopa Troopa who got a Mega Star. He appears in Super Paper Mario, and Mario/Peach/Bowser/Luigi have to find a Mega Star for themselves to defeat him. It is found in level 3-2 and you must run away or he can do serious damage. Fighting is futile as Mario is too small to even jump on him. The only way to defeat the Mega Koopa is to grab the Mega Star at the end of the level.