After talking on discord, we will go with the phoenix! Waver will be able to turn into a pigeon sized phoenix. Along with this, he'll have the following abilities:

Resurrection: Whenever he is badly injured or dying, Waver will burst into flames. From the ashes, he'll revive in his phoenix form (with ugly baby feathers). He'll have to spend a day in this form as his feathers grow back in before he can return to his human form. It is up to you to decide what qualifies as "badly injured".

Flight: He is able to fly at an average bird speed.

Tiny Fire: He can conjure fire proportionate to his phoenix size. Which means like a lighter size.

Enjoy your new feathery life Waver!!