Having been inspired by Marvel: Ultimate Alliance, I was wondering if anyone else has considered having costumes be a non-trivial part of a character.
(For those of you unfamiliar with Ultimate Alliance, in the game each character has four costumes, each of which bestow different (upgradable) bonuses to the character).
My first inclination would be to have each costume have 3 separate abilities (either actions or modifiers) that the character can only access while wearing that specific costume. On some level this would make sense (the "Iron Spider" has extra arms, more sensors and other goodies), but on the other hand it requires keeping up an inventory of which costume the character has and how each costume's abilities advance.
Costumes would not reflect a huge difference in character, but rather some minor new abilities, or skills which a character tends to use more than while wearing other costumes.
To an extent, I've thought about it, mostly regarding the different Iron Man suits. I think it would make sense depending on the character, and costumes would be acquired in-game rather than at creation (generally). Kind of like how Spider-Man with the symbiote suit could be considered a costume upgrade that the player abandoned after a while due to the negative impacts weighing down the positives of the suit. The costume wasn't part of character creation, but it created enough challenge stones within itself to warrant Spidey being able to have the new abilities.
I like the idea of gaining new suits throughout gameplay like Spider-Man, but in the case of Ironman, he created all of his suits. The different costumes could go either way. Wouldn't this basically be like a weaker equipment based version of Transform Self? Still an good thought considering situations like the symbiote costume and Ironman's other costumes. Perhaps this would just be something the individual GM would have to decide on. After all, Spider-Man didn't choose to take the symbiote. And Ironman had to invent his other costumes and there is already an action for that.
I would say that if a player wants to pay for different equipment with different advantages, thats his perogative. Things that make major changes to ones capabilities could still be done... as long as you can afford the stone cost. The changes made by changing costumes in Ultimate Alliance are very dramatic. For instance, Wolverine doesn't even Regenerate any faster than other heroes in some of his costumes.
All of that being said... for something like Spiderman and his symbiote, that should definately be a GM discretion thing, most likely occuring when a player takes a new challenge like "new powers bring new problems" etc.
Perhaps you could take abilities or modifiers with a disadvantage of it being attached to your equipment. If you aren't wearing the equipment, you completely lose the capacity to use that power so it should be slightly cheaper. Actually that kind of goes along with the main book's disadvantages: Takes extra time to prepare (-1 CL)(because you have to equip the costume), and power out of control without device (-2 CL) or power weaker away from power source (-2 CL). Or perhaps you might treat like powered armor with the need to supplement your abilities and use A.I. It just has some cheaper abilities and allows you to take it off.
Honestly, I would just say to write up different CADs for each suit. Keep the base CAD the same (basically everything that you have without the suit) and then balance the rest out. You could have one CAD that's for your combat suit (20w dedicated to the suit), one that's for stealth (the same 20w redistributed for the stealth), etc. It really isn't quite the same as Transform Self, after all, as you can transform whenever you want during a mission. With costumes, you pick one for the mission. No reason you should be underpowered because you have multiple costumes. I just wouldn't really recommend something like this for team play, seeing as team play is all about having different people fill all the important roles. One person who can choose to be any role in the beginning of the mission defeats this purpose.