From the Super Mario Wiki
Hotheads are large balls of sparking energy that first appear in the game Super Mario World.
Super Mario World
They slowly move around platforms and don't pose much of a threat. These creatures only appear in a few fortresses and castles. They can usually be found in areas with Li'l Sparkys, which are essentially smaller versions of Hotheads.
Super Princess Peach
The Hotheads reappeared in Super Princess Peach, where they served the same purpose.
Super Smash Bros. Brawl
Hotheads have made another appearance in Super Smash Bros. Brawl as an item. The Hotheads, just like in Super Mario World, will stick to the stage when thrown and burn anyone that touches it. It will also grow larger if it's hit with attacks, but it grows significantly larger when hit by Fire attacks, maxing out at approximately 3 times its original diameter. Hotheads move quickly around the platform they are on, but can also just fall off entirely.
Trophy information from Super Smash Bros. Brawl
|| SNES Super Mario World
|| An item that, when tossed, sticks to the terrain and moves, causing damage to those it touches. Whoever threw it won't take damage. It will grow larger if it's attacked, which ups its attack range. However, an increase in size corresponds to a decrease in the time it stays on the screen. A really big Hothead will take up the entire screen, and is quite a sight to behold.
Names in other languages
|From パサパサ pasapasa, meaning "the state of being dried out" and 爛爛 ranran, meaning "flaming"; officially romanised as "Pasaran"
||Großschein (since Super Princess Peach)
Hothead (Super Mario World)
Sfavillo (Super Princess Peach)