Similar to Deft Focus, X-Gene is an efficient resource upgrade that can't be built around because it only pays for cards that come in your hero's identify-specific card set. Among the mutants we have so far, here is how many identity-specific events they have that cost at least 1 resource and a comment on whether or not I would play it in their deck.

Wolverine (10) - Sometimes play. Despite having the most eligible events, there are two mitigating factors. 1 - Wolverine often spends all game in hero form, making this unplayable except on turn one. 2 - He can play one attack event per turn with the claws, so you can't use X-Gene as often as you like. Still such a high count of other events that it's reasonable to play the Gene.

Rogue (10) - Always play. Rogue needs all the help she can get setting up economy

Storm (9) - Always play. High count and powerful events. No-brainer

Phoenix (8) - Usually play. A bit hard to make use of early, but once you're unleashed, your events are your best cards.

Shadowcat (7) - Usually play

Gambit (7) - Usually play

Cyclops (6) - Usually play. Cyclops decks are often high-synergy and based around allies, so off-theme card slots are slim. That being said, Cyclops goes through his deck really fast, and Phoenix can grab an event back. I like it here.

Colossus (3) - Rarely play. It only pays for Steel Fist

Even with Colossus, X-Gene is never embarrassing to play because it takes only 2 uses to break even on resources, and you can often use it the same turn you play it. This card will be a staple of X-Men decks.

It's not enough to only look at how many events a hero has but you have to consider the use restrictions. A lot of identity-specific events for the Mutants currently released also have the Superpower trait so often the deck has to decide between X-Gene and Deft Focus. There's also the option to play both but that's not always the case. There are three main differences in how these two cards work and these differences will inform whether the deck wants to play them:

1. Deft Focus is a Hero Action so you have to be in Hero Form and you can't use it to reduce cost of cards in the Villain phase. In other words, this isn't usable for Defense events like Flash Freeze/Bulletproof Belle.
2. X-Gene can't pay for non-Event cards. So you can't use it to pay for Organic Steel/Iron Will/etc.
3. X-Gene is only playable in Alter-Ego. So unless you draw it in your opening hand/mulligan, playing it later requires a trip to AE which not every deck can/want to do on demand.

These are the number of cards that would be affected by either cards for each of the current Mutants:

• Colossus: 3 XG, 7 DF. Deft Focus is better than X-Gene especially since Colossus has access to Limitless Stamina.
• Shadowcat: 7 XG, 9 DF. Deft Focus is better than X-Gene. Shadowcat isn't likely to swap to AE often and will have a harder time playing a late X-Gene.
• Cyclops: 6 XG, 3 DF. Would not play either. Cyclops is often in Leadership and neither pays for Allies so the space is better used for something like Team-Building Exercise.
• Phoenix: 8 XG, 0 DF. X-Gene is an option although I would play Team-Building Exercise over it as TBE helps her pay for Cyclops or other X-Men allies and her Psionic Upgrades.
• Wolverine: 10 XG, 5 DF. Would not play either since you're rarely paying for his attacks with resources so these would often be unused.
• Storm: 9 XG, 7 DF. Storm wants both cards since her events are all very powerful and expensive.
• Rogue: 10 XG, 8 DF. Rogue wants both cards since she has a bad economy.
• Gambit: 7 XG, 5 DF. X-Gene is better than Deft Focus.