Ability to throw fire charges from your hands and a heat potion.

The first one is pretty self-explanatory, so I don't think I need to explain it. However, the "Heat Potion" would be a new potion crafted using a fire charge at a brewing stand. It would apply a "Heat" effect—similar to the freezing effect, but instead of slowing the player down, it would deal frequent damage akin to burning. It would also shift the heart icons to warmer tones and cause burning particles to emanate from the player. You could avoid this damage by jumping into a water source; interestingly, if a player were affected by both Heat and Freezing simultaneously, they would take damage from neither. The Heat effect could also potentially be triggered by a specific block—much like Powder Snow—though I don't have any ideas for that yet.