It works GREAT for a villain in my experience. You can taunt the players with their own words, or give ominous hints that they know wont be expounded upon.

Kenku played RAW gets old quick

Iirc heat metal doesnt work on magic metals like mithral and adamantium anyway

Id like to use my reaction to change underwear

The Gobbler - CR 20 Only takes slashing and fire damage, gobbles your points

Thats just squiggs from warhammer