The Meaning of Life, the Universe, and Everything.
The phoenix is a fireproof mob from the mushroom island biome, which has 6 wings, a pair of leg wings, a raptor tail and a junglecock head. It is white, and has a mushroom coming out of its back. It can run fast, jump high and glide. It can be tamed by giving it cooked chicken. It will jump on a player's head when tamed, and will put out the payer and steal their damage and debuffs. It can also heal itself slowly. It will attack things that attack its owner, and can remember attackers for 7 days. It can be bred with seeds, and does not need a partner. It drops a phoenix egg when killed, which can be crafted into a phoenix spawn egg. The phoenix spawned will be as tame as the phoenix it came from.
Recipe for Phenix spawn egg (Spawn egg represents phoenix egg):
This is pretty interesting, but I agree with Reeper for the phoenix to be a Nether mob. The overworld one can be called a shroombird or shroom coatl or something, and it will get rid of your debuffs, as you stated. Pretty useful, and not too overpowered.