From the rules sheet,
When you play a Hero card that says it transforms into another card, you complete all effects on the card you played and get its normal * and ///.
Then remove the transforming card from the game (putting it in the transformation Pile) and put the newly transformed card into your hand instead (from the Transformation Pile). You can play the new Transformed card immediately that same turn.
Some transforming cards tell you to put the new card on top of your deck or in your discard pile instead.
Many of the transforming cards go into your hand. You get an exceptionally good hand once, then just keep the transformed card thereafter.
Others put the transforming card into your discard pile (like you recruited it) or on top of your deck (like Wall-Crawl). If you have the means to draw it, yay! If you have the appropriate X-Gene from the X-men set, yay! But you don't otherwise get to play it this turn.