Technically this card could be read as :

Before the start f the game, you must spend 2 ER then replace this card with an Identity Specific ally and shuffle it to your deck.

Some IS Ally are worthless with this because they work specificly with their hero, using their gimmick.

But you can have in every deck Black Cat, Captain Marvel, Mantis … You could go Sidekick with them …

The possibilities are impressive … for a cost. You are forced to discard two cards which slow down your first turn a lot. I really want to test that card to se if the cost is Worth the reward.

But yeah, I really want to try this card, to see what broken combo can be made by adding an ally to a hero that shouldn't have it.

The mind reels at how different hero-specific allies could work with other heroes. Some are so directly tied to the specific hero that they're not of much benefit. But others....

1. Shuri from Black Panther Core Set: "Response: After Shuri enters play, search your deck for an upgrade and add it to your hand. Shuffle your deck."

The vague text from the Core Set is to everyone's benefit. All heroes have hero-specific upgrades they want to get into play. Beyond that, any upgrade-focused build (i.e., voltron ally) will benefit from Shuri's ability.

2. Spider-Woman: Jessica Drew from Captain Marvel Core Set: "Response: After Spider-Woman enters play, confuse the villain."

Two cost, 2/2/2 stat line, confuse the villain. A discount Professor X with damage output. All around a solid addition to any team, especially heroes that want to flip down to alter-ego.

3. Angel from Psylocke hero pack: "Response: After you play Angel from your hand, ready your identity."

Ready any identity, in hero or alter-ego form, when played from hand. Ready-up builds, here we come. Also has the Aerial trait, so great for Flight Squadron decks. You can also get Angel in an Uncanny X-Force deck since the basic Angel ally is X-Men traited.

4. Mockingbird: Bobbi Morse from Hawkeye hero pack: "Interrupt: When the villain initiates an attack against you, spend 1 resource of any type and return Mockingbird to your hand → prevent all damage from this attack."

Three cost, 2/2/3 stat line is well above average. Double-traited Avengers & Shield, so works in both tribes. Free block and a resource sink for resource-heavy Leadership decks.

5. Ms. Marvel from Nova hero pack: "Hero Response: After you play an event, exhaust Ms. Marvel and deal 1 damage to her → return that event to your hand from your discard pile."

Event heavy heroes, especially Gamora, like this, as do low hand-size heroes.

A couple of more allies to consider pairing with this card:

 Colossus from Magik's kit: He can defend from hand with tough without exhausting

 Amadeus Cho from Herc's kit: 2 cost ally that can exhaust (no damage) to draw cards. Yes, you have to protect him from 
 minions, but if you get him early, that could be a TON of card draw