We don't know much about this character, only that he was delivering pizza to Martha Sutherland when the changes accured.
Steven Gray is very much like our Peter Petrelli but with a small difference, our knowledge tells us that Peter is a empathic mimic that needs to feel his connection for ability recall, where as with Steven its different, yes he mimics but he mimics like a battery!
When he is with some one with an ability or feat like Peter his DNA reconstructs it self to portray the ability/feat of the person(s) around him but does not keep it like Peter does..
Steven absorbs like a battery charging the ability, but only when the ability is being used or active, so in basic demonstration if Steven was to be standing next to some one like say ..Clair Bennett, unless her ability is active, then firstly if he was to become injured it would take time for the wound to heal, where as if he was around Clair a longer period of time the wound would heal instantly and longer he would become unharmed completely, and as soon Clairs ability is inactive he would start to loose the ability/feat and in time would become completely normal again.
We're unsure of the speeds and whatnot of the mimic and loosing of the ability/feat or if he can handle multiple abilities, i guess in the future we'll find out.

Following a Schitzophrenic attack where the two personalities manifested, one would charge just the one ability where is the other would mimmic many but the more abilities he gained at the time the weaker they became. After Comming out of the episode and finding help from some one unknown was able to force the two personalities together and become healthy again, loosing the ability to charge gained feats but kept the ability to mimmic multiple abillities but gained the fall back of the more gained the weaker they became.