[quote=@Sep]
<Snipped quote by Fallenreaper>

Kinda tempted to go the opposite route and go he can take more than one, then later he limits it to one... as that adds new problems. I'll decide later, obviously animals will be easier than supers abilities as animals he can pick and choose what he wants.

He's limited to abilities that don't require an actual physical change. I.E. He can get strong off someone, but if someones ability is to turn into an animal that's pretty much useless to him. Magic as well, can't be copied. So long as the magic hasn't actually altered the persons DNA in any way. This is just a possible, I'm also interested to maybe do something along the lines of Beast Boy but I'd need to think on how I'd make that work. I'm definitely going to do one of the two ideas.
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IF you go the beast boy route, there's actually at least two ways that can be done: 

One- He has to have seen the animal in order to acquire it's shape, abilities, etc. Including using those set abilities or skills. 
Two- Doing it similar to the animorphs, which was acquire the animal through touch and being able to access the animal by focusing on them at any time.  

Despite how corny 2 sounds,the books and even the show did it fairly well. Even had a weakness that if they stuck in the morph for up to two hours, they risk being stuck in it and unable to morph out. (though I would suggest in this story it might be better to adjust it that the longer he stays in the animal's shape, the more he becomes like that creature and so might be something of a character struggle or conflict with the power) The morphing also wasn't instant but took seconds or minutes depending on how complicate and radically different the creature was. In the books, morphing humans was complicated (save for Tobias who become trapped in the hawk's body and later regained the ability to morph later in the series) and so was heavily avoided. In addition, just because they had a wide range of animals didn't mean they used them all and some were even re-acquired due to how long ago they gained them... Gods, my inner nerd is seeping. XD