This is the latest in the series of cards with a similar effect; 2ER upgrade, Response: satisfy a condition, discard this card > ready your hero, such as Battle Fury, Justice Served, or Indomitable. Ready to Rumble is basic so it complements any aspect. Every hero can satisfy this by flipping from alter-ego form to hero form. Heroes that like to flip such as She-Hulk can find a use for this card. Heroes with multiple forms such as Spectrum or Ant-Man will get the most out of this card. As more flipping heroes are introduced this card will increase in value.

The way to look at this card for heroes that don't have multiple forms is basically to consider your REC + your hero stat activation for the cost of 1 and the card. That is not too bad for those using their basic REC a lot. You can start a turn in alter-ego, regain some HP, then flip and ready to also use a basic stat. It goes very well with Down Time and THW/ATK boosting abilities. It's good in that you can play it and then use it whenever you like, you are not forced to do it asap.

Alternative uses include alter-egos with some kind of exhaust ability. I love this on Ms. Black Panther. Having the ability to exhaust to play an upgrade, then immediately flip to hero form, ready and use that upgrade via a basic power can be very good. Shuri has Queen Ramonda to do the REC for her, so exhausting to play an upgrade and then use it immediately is nice tempo.