Sliding into these enemies will turn them into odd-looking sprites as they die. Though it's just a graphics glitch, it looks like Mario totally smashed that enemy!

• Iggy and Larry Koopa's fireballs: Let these Koopalings chuck a fireball at you, then slide into it.
• Grinder: In Forest Fortress, slide down the Triangular Blocks into the Grinders.

If you have a Game Genie, use an unlimited invincibility code to see similar effects when you kill stuff that's not supposed to be killed, such as Blarggs, for example.