A phoenix from the Potterverse feels like the perfect pet for those people that practice ‘one-upmanship’. Those sort of people that always have a more impressive anecdote locked and loaded as soon as your story is finished. Or those children that make up new rules for games on the fly so they don’t lose.
Your dog is very cute, but my bird can heal me when it cries. And its singing is magical. Aaand it’s super strong. Aaand…
Dungeons & Dragons already has a phoenix. It’s a gigantic elemental, always on fire and (presumably) always angry. Just a mass of fiery feathers. Nothing like the little, Deus Ex Machina that is Fawkes. Though the Potterverse Phoenix lacks the scale of their counterpart, it has a colourful array of abilities to aid the adventuring wizards out there.
Fawkes

Most of the stat block is based on the brief description from Fantastic Beasts. The Fiery Rebirth is a miniaturised version of the ability the D&D monster has (not quite not the 60-foot wide, 4d10 detonation). The Healing Tears is a very powerful move, but the tears nullified basilisk venom so I don’t think I’ve gone overboard.
I’m particularly happy with Phoenix Song. Not only is this a great support buff, it could also provide for some interesting RP moments if someone in the adventuring party is secretly ‘lawful evil’… or not as good as they thought they were.
There are some extra abilities, not mentioned in the book, that show up in the movies. The inexplicable carrying capacity, and the fiery teleport that got Dumbledore to safety, are both covered in the stat block.
One detail which I added, for very deliberate reasons, was labelling Fawkes’ creature type as ‘monstrosity’. This phoenix fits the description, and the fact that this phoenix is not made of fire all the time means that ‘elemental’ doesn’t fit. The main reasons was to avoid labelling Fawkes as a ‘beast’. Beast is a creature type that can be magically summoned in a variety of ways. Part of the draw of the phoenix is its mystique, its rarity. Having every adventuring party able to summon them daily spoils the majesty somewhat.
Thank You For Reading
If you want all the Fantastic Beasts in your D&D game, look here!