Blitz Chainsaw

While attuned, you have proficiency in chainsaw weapons and you cant cast spells.
Rev:
While in initiative your weapon can gain heat.
When you make an attack with this weapon you can choose to gain 1 heat, when you do, you deal an additional 1d12 lightning damage. If your turn ends and you haven't attacked a hostile creature since your last turn or taken damage since then your heat is reduced by 1. You can also reduce your heat by 1 on your turn as a bonus action.

heat:
While at 4 heat this weapon counts as a +1 weapon and deals an additional 1d12 lightning damage
While at 8 heat your walking speed increases by 5ft snd you deal an additional 1d12 lightning damage.
While at 12 heat you attack with a +1d4 to your attack rolls and you deal additional lightning damage equal to your proficiency bonus.
When you reach 20 heat, you gain an additional attack action this turn and your heat becomes 0 at the end of your turn.

Rarity

Very rare exotic weapon (Requires attunement)