I'll start by discussing the overall power level and play style of Phoenix and her identity-specific cards. Later in the review, I will identify some of the different ways to build Phoenix that play to her strengths, and I provide links to the most popular decks on marvelcdb for each of the aspects.
---------------------------------Overview ---------------------------------
Phoenix starts the game with the Phoenix Force upgrade in play, providing 4 free resources to be used once per phase. She starts as a 3/1/2 hero, but once the 4 power counters are depleted, she becomes UNLEASHED, shifting to 1/3/2 stats and powering up her events. The decision to unleash or not is rather complex and may change game to game.
Strict Upside - the powering-up of Telekinetic Attack, Psychic Blast, and Telepathic Trickery
Strict Downside - the worsening of your obligation, Burning Hunger, acting as a second Shadow of the Past to put your nemesis minion Dark Phoenix and side scheme Consume the World into play.
Grey area - the shifting of stats, Phoenix Suit, and the tension of whether you want to use resources inefficiently just so you unleash faster
In general, I find myself unleashing as fast as possible to power up those events, but knowing when to slow down because your THW is more valuable to the table or you really want to save that last power counter for a more efficient turn is necessary to maximize the skill of playing Phoenix.
With the starting power counters and strong unleashed cards, Phoenix is strong in both the early game and late game, making her one of the strongest X-Men heroes in my view. She struggles with having several highly situational or weak identity-specific cards, but being smart with your deckbuild and mulligan can mitigate that issue. She also has a devastating nemesis minion, Dark Phoenix, that even gives you a new way to lose the game in Consume the World. This can be a frustrating play experience that turns some people away from Phoenix, but if you want to play her you'll just have to take the good with the bad.
---------------------------------Identity-Specific Cards---------------------------------
Cyclops - At his best when you use up the bonus 2 power counters before being forced to remove them when Cyclops dies. A solid ally, but you might not want to play him early if you are racing to become unleashed.
Mind Control - a phenomenally powerful card, worth taking up almost your whole turn. Mutant Genesis abounds in Sentinels and Acolytes that provide insane value for this card, which effectively defeats a minion and plays your own ally version. The icing on top is that any "When Defeated" abilities on the minion are turned blank.
White Hot Room - a strong resource generator with a nice fallback of healing if you're still trying to get unleashed or have enough counters already
Phoenix Firebird - the best way to race to zero power counters if you are trying to unleash. The second mode is neutral on resources, but lets you store them or get back to restrained form if you want.
Telekinetic Attack - the least necessary to upgrade by becoming unleashed, but a serviceable version for Phoenix's "Web Kick" card
Telepathic Trickery, Psychic Blast - the real payoff to becoming unleashed. Not unplayable when restrained, but priority #1 when you're unleashed is to see these
Rise from the Ashes - On the expensive side, so hard to fit in if there are encounter cards to answer. A very powerful effect though, that could represent 12-ish healing if killed from 1 life.
Telekinetic Shield - A nice safety net for damage. Not a crucial card but gets the job done
Mental Paralysis - I don't think I've ever played this from hand. Just use your resources to kill the minion (or Control it)
Phoenix Suit - Another one that's not a priority. Steady doesn't discard statuses, so once you unleash you will still be stunned/confused. Retaliate is marginal as well. Aerial can enable some strategies, but hard to get behind using your resources just for that.
---------------------------------Strategies---------------------------------
Psionic
The psionic trait makes Phoenix one of the few heroes that can play the psionic cards: Psychic Manipulation, Psychic Assault, Psychic Misdirection, Psychic Kicker, Psi-Flail Strike, Psi-Bow Attack, Telekinesis, Telepathy.
And while technically playable by any hero, Psimitar and The Power of the Mind are at their strongest with the 9 Psionic cards in Phoenix's identity-specific set.
Side Schemes
Phoenix is one of the only heroes in the game to start with 3 THW. This enables turn 1 completions of the powerful 3-threat player side schemes Build Support, Call for Backup, and Superpower Training, the last of which can be left out until you have the perfect minion to Mind Control. Phoenix makes a great Justice hero in general due to the combos with thwart-completion cards like Turn the Tide, Overwatch, Chance Encounter, etc., since thwarting is a fantastic use of Phoenix's basic power.
X-Men
With the Psionic trait and being an X-Men herself, Phoenix is the best hero for a Cerebro deck. This lets you play a toolbox of the strongest X-Men allies like Professor X, Beast, Polaris, and silver-bullet style allies like Sunfire and Magik to be drawn exactly when you need them. Use X-Men Instruction to shuffle back in the specific ally you want to find if it's in your discard pile. There is no shortage of other X-Men archetype cards like Danger Room, Utopia, X-Mansion, "To Me, My X-Men!", and Uncanny X-Men to take advantage of a deck full of X-Men allies.
Villain Phase Events
Phoenix's power counters can be used as resources once each phase, not just once a round. So if you want to play some defenses like Side Step or Jump Flip, you can use your power counter and help yourself unleash faster. Some of the Psionic cards like Psi-Flail Strike and Psychic Manipulation are played during the villain phase, giving more options for this strategy. You can get even crazier and try Warpath out, playing your normal events in the villain phase.
---------------------------------Top Decks---------------------------------
(the most popular decks always come about shortly after release and might not reflect the most powerful up-to-date versions. In this case, many of these decks would probably play Psimitar and/or The Power of the Mind had they been out at time of publishing)
Justice:
- This deck by Andrahil leans heavily into the X-Men support and the Mission Training + Game Time combo. Psychic Manipulation also makes an appearance. This is a very strong thwarting deck and probably wants to unleash quicker than most to compensate on the damage side
Protection:
- This deck by VillainTheory cleverly uses Pinned Down to keep a minion around to receive the attack from a Psychic Misdirection, a very powerful but normally hard to use Psionic card
Aggression:
- Aggression is a common choice for Phoenix due to Psychic Assault being one of the best and simplest to use Psionic cards. MegiDolaDyne's deck is extremely new player-friendly, requiring only the Core Set, Mutant Genesis, and Phoenix packs.
Leadership:
- Journeyman2 offers a Vision-based Voltron deck using the Psionic leadership card, Psychic Kicker. The X-Men twist on Voltron with Danger Room Training and Game Time is also very exciting.
---------------------------------Conclusion---------------------------------
Phoenix is a unique, fun, and powerful hero whose Unleashed/Restrained mechanic makes every game a different puzzle to solve. Thanks to her high starting THW stat and Psionic trait, she can be built in ways that make you think beyond a simple stock list for each aspect. I recommend picking up the additional Psionic theme cards in the Next Evolution box and Psylocke pack. The X-Men archetype cards are spread across many packs, but one I would highlight is the Cyclops pack for Utopia, Game Time+Danger Room Training, and one more X-Men ally of each aspect.