Movement and Neutral Options
Mixup Theory
Oncoming Mixups
Counterplay
Dark Phoenix as a character, once fully activated and allowed to set up her offense, is extremely oppressive and heavily favored to win the match by herself. Players have developed a variety of strategies to prevent this from happening, with various levels of in-match consistency.
Guard Break Setups
When Phoenix dies with five bars, her Dark Phoenix activation places her in the air slightly above her location when she died. This means that a player who has Phoenix in a kill combo has some leverage to cause her to activate at a specific position. This is can behave similarly to an Oncoming Mixup, except that Dark Phoenix does not have any of the usual throw immunity when she awakens, making her much more vulnerable to being Guard Broken. This is the most consistent method for dealing with Dark Phoenix on teams that have access to it, as it is entirely in your hands to execute the strategy once you have hit Phoenix.
One small additional detail is that, although Dark Phoenix Rising will almost always place Phoenix airborne (even if she died while grounded), it is possible to force her to activate in a grounded state if she is knocked down and killed with a late-hitting OTG attack.
Characters with notable guard break potential include:
Anti-Air Command Grabs
Spider-Man's Ultimate Web Throw is an anti-air command grab hyper with enough range to grab Phoenix from outside the range of her activation shockwave. Spidey can consistently land this setup from most combos by killing with Maximum Spider, activating X-Factor as soon as the cinematic ends, and immediately going into Ultimate Web Throw. Other characters can also kill Phoenix and DHC into Ultimate Web Throw if Spidey is on the team. Video Example
She-Hulk's "Taking Out the Trash" hyper is an anti-air command grab hyper which has enough invincibility to blow through Phoenix's shockwave and grab her. She can kill with a variety of moves and X-Factor cancel into the hyper, or have another character kill with a hyper and DHC to her.
Frank West also has access to an invincible anti-air command grab with "Funny Face Crusher" as long as he is at least Level 3. He can set this up off just about any kill while grounded by doing Kill Move > LMHS, X+S > 623XX.
Spencer has an anti-air command grab in Jaw Breaker (623H). If Spencer kills Phoenix with Bionic Maneuvers (236XX) midscreen, the hyper's cinematic ends in such a way that Phoenix will pop in the perfect position for Spencer to grab her from outside of the initial shockwave range. Video Examples.
Nemesis has an anti-air command grab in 63214M with enough reach to grab Phoenix from outside the range of her shockwave.
Skrull has a similarly long-ranged anti-air command grab in 214M.
Both Thor and Haggar have 1f Aerial Command Grabs in their respective j.63214H specials.
Haggar also has an Anti-Air Command Grab if he kills on the ground in 623H.
Unblockable Attacks
Shuma-Gorath has an Unblockable attack via his Chaos Dimension 236XX Level 3. Shuma can combo into the activation bite of Chaos Dimension, continue the combo afterwards to kill Phoenix, then X-Factor and mash H to eat Phoenix as she activates.
X-23 has an Unblockable attack via her Silent Kill 214XX Level 3, similar to Shuma. However, X-23 has a harder time comboing into her Unblockable hyper than Shuma does.
Firebrand can force Phoenix to block a meaty attack on awakening, usually either an assist or THC, while charging his Unblockable 623[H] Demon Missile attack. Depending on the meaty attack used, Phoenix may be able to escape this with an X-Factor Guard Cancel into teleport or other mashed move.
C.Viper can fully charge an X+S Focus Attack to make it Unblockable and, as a bonus, the armored property of this move will allow it to beat Phoenix's shockwave on awakening. However, the very limited range on Focus Attack can make practical setups into this move difficult.
Taskmaster also has an Unblockable attack in the Headbutt followup to his Sword Master attack (623X>H). Like all Taskmaster unblockable setups, it is vulnerable to a well-timed pushblock on Taskmaster's sword swing, but a sufficiently fast multi-hitting attack from a teammate can keep Phoenix locked down and make timing this difficult.
Phoenix Wright can force Phoenix to awaken into a meaty Steel Samurai Maya (236XX) hyper, activate X-Factor, and then land a High/Low Unblockable by connecting an Overhead attack at the same time as Maya's Low hit.
Besides these specific setups, any number of characters can kill with a Team Hyper Combo, then X-Factor to move freely while Dark Phoenix awakens into meaty attacks from the assist characters and attempt to mix her up. Video Example.
Meter Steal
It is possible to prevent Phoenix from activating Dark mode, even if the Phoenix team is successfully able to build all five bars, by using one of a handful of methods to lower the opponent's total meter below 5 full bars before Phoenix is able to die.
In a vacuum, every character has access to a universal way to remove meter from the opponent via Side TAC, so long as the team still has at least two characters alive to perform a TAC at all. As a general rule, Phoenix players can simply mash a Side TAC break while being aircomboed to prevent their meter from being stolen this way. By using a TAC Cancel, characters can fake out with a TAC in a different direction, and then cancel to a Side TAC in order to steal one of the Phoenix player's bars. This does not guarantee a successful Side TAC, but does force the Phoenix player to read that a TAC Cancel will be attempted and guess correctly.
As discussed on the TAC Cancel page, all characters can perform a TAC Cancel if they have X-Factor available, by performing TAC (Up or Down) > X-Factor > TAC (Side). Additionally, a few characters are able to airdash-cancel the startup of a TAC if they link into the TAC attack from a neutral state. These characters are Zero, Chun-Li, Morrigan, Spider-Man, and Shuma. Shuma can only land this airdash-cancel if he is brought in via a TAC from another character first. These characters can also perform the X-Factor TAC Cancel like normal, or even perform both in the same sequence for a "Double TAC Cancel", which is extremely unlikely to be read correctly.
A handful of characters are able to take advantage of a technique popularized by MarlinPie in which you intentionally whiff a TAC in the Up or Down direction, baiting out the opponent's TAC Break attempt, then recover and still land a Side TAC before landing. Doom and Nova are both able to perform this setup, and other characters with 8-way airdashes likely can as well(?). Video Example.
Besides this universal option, the only other practical way to steal an opponent's meter is Morrigan, whose Soul Drain (236S) projectile steals 30% of a bar on hit. Morrigan can fairly consistently combo into Soul Drain by scoring a Hard Knockdown, throwing out a Soul Drain, then canceling the recovery into Shadow Servant (623XX). Video Example The OTG hyper will lift Phoenix up into the fireball, hopefully stealing her bar in time before she dies. There are also a variety of other methods for comboing into at least one Soul Drain, including DHCs to Astral Vision, using assists to cover its startup, and using X-Factor cancels into it. Morrigan can either connect one Soul Drain just before Phoenix is about to die in order to deny the transformation, or intersperse Soul Drains into her combos and fireballs throughout the match in order to keep the opponent's overall meter low and make it harder for them to reach 5 bars in the first place.
Besides Morrigan, the only other character with non-TAC capacity for stealing meter from the opponent is Shuma, whose regular ground throw and airthrows steal 20% meter on success. Because you can not combo into Shuma's throws (obviously), this represents a much less practical option.
Snapping Phoenix in Early
The most straight-forward approach. Phoenix is almost always kept in the Anchor position to maximize the amount of time her teammates have to build meter before she is brought in. By using a Snapback, you can force Phoenix into the point position early, giving yourself an Oncoming Mixup and a chance to kill Phoenix well before her team can build the necessary meter.
Unfortunately, Phoenix has some of the best tools in the game for dealing with Oncoming Mixups. She has access to an 8-way airdash, a teleport, and access solid Throw Tech OS in j.H. Even worse, she has access to Phoenix Rage (236XX), making her one of very few characters in the game with an Air-OK invincible hyper, giving her an option to blow through meaty oncoming setups. That said, getting Phoenix to spend a precious bar on an invincible hyper to protect her incoming is a small victory itself, and she may need to spend a second meter later in order to safely DHC out. Oncoming Mixups for dealing with Phoenix should ideally be prepared to deal with all of these options.
Timer Scam
tldr don't try it.
In theory, if you have eliminated both of Phoenix's teammates and have a significant life lead, you can circumvent the need to kill Phoenix at all and avoid any risk of dealing with her Dark form by winning on time. If you simply refuse to actually attack Phoenix and run away for whatever the remainder of the match timer may be, an assist-less Phoenix might not be able to chase you down effectively enough to make up the difference.
In practice, this has been tried by a few different players at various points in tournament matches and has an extremely low success rate. non-Dark Phoenix is actually a very competent Point character when you ignore the disadvantage of her terrible Health (which instead becomes a distinct advantage when her goal is to get herself killed). She has great mobility and solid potential for both chip damage and mixups. Since you are unable to threaten Phoenix with meaningful damage while running away, there is nothing to stop her from rushing you down with repeated throw mixups until you crack, and so beating Phoenix on time is not really any more practical than winning on time in any other context.
A handful of characters have "timer scam" infinites, infinite combos with low enough Minimum Damage Scaling and base damage that it would take them an impractical amount of time to kill any normal character. Notable examples of this type of infinite include Dante's TAC Infinite, Nova's Timer Scam TAC Infinite, and Spencer's non-TAC "Zipfinite". If you have unwavering faith in your execution skills, you can bleed out upwards of 70-80 seconds killing one of Phoenix's normal-health teammates using one of these infinites, securing a win without having to interact with Phoenix at all.
