"You are immune to heat damage"
Heat absorbtion is a physical mutation that is currently in unfinished content. Because of this, you cannot get it at character creation. You can get this mutation if you allow unfinished content in options, and use this wish command for it. With heat absorbtion, you are immune to heat damage and get health back for .1% of that damage. It rounds up for the damage, so if you ae on fire, you gain 1hp back every step you take. Every time you level heat absorbtion up, you heal for .1% more to get to .2% and so on. Similar to Cold absorbtion.