Burning

The Burning debuff is a detrimental effect to a player's health. The Burning debuff can be inflicted on the player by some mob types as well as some environmental tiles, like lava, and damages the player's health by 3 every second for its duration.

Caused By
Many enemies in the Underworld and some in the Crypt can inflict the Buring debuff on the player if their attacks hit, Wading through lava will also burn the player constantly until they step out of it.

Prevented By
So far only an Obsidian Potion will make the player immune to the Burning debuff, but only while the effect of the potion lasts. Obsidian can be found in plentiful numbers within the Underworld