Firstly, I'm gonna go over the weird weakness stuff. It's fucking ridiculous to believe that fire form can be weak to a chilly environment, but immune to say, a blast from Mr. Freeze's ice gun, because ice is super fucking cold.
Traditionally, elemental creatures and armor are resistant (but rarely immune) to their element, but weak to its opposites, not resistant to both.

This brings me to my second point: Do not write out all your weaknesses. Holy shit, dude. I know this is a high powerlevel thing but writing yourself as invincible is pretty bullshit, ESPECIALLY when it's a switch you decided to make mid-game.