He needs to doppelgangers for business reasons. Don't be mistaken, his clones can be killed like any other human, but like any other human, they will put up a fight. Now the clones of the clones on the other hand, they're nothing to worry about as long as they don't get a jump on you. But yeah, he doesn't "need" to invest a lot of mass or intelligence if he only needed them for a one off thing like someone to play distraction or something, but if needs them to do something like, say, spy on the competition or run one of his stores, he'd need to give his clone a lot of mass and intelligence so it can do the job properly.

As for what he's made of, it's a sort of Tar like substance that can harden to a likeness of cement or soften to a more maple syrup texture. I wanted to make him have a weakness towards fire, but than I thought "Well yeah, everyone tends to die when they're lit on fire". Logical weaknesses and all that. So instead I was thinking maybe give him a sort of EMP weakness, you know, like electricity is particularity effective at weakening and killing him. But I didn't want anyone mistaking him as a robot or anything. I guess I should add more weaknesses, since it's not like you could cut off his head or anything.

As for hosting dead bodies, it's a bit complicated how he does that. As I said, he is a tar-like substance, i.e. a liquid. To "Take over" a dead body he basically becomes the body's new blood. And trying to fit all of him through a dead persons' veins is more work than it looks. If he needed to look like someone he'd rather use a skin suit, or even better, take on a vaguely human form and use his illusions to make up the details. When I said he could "Fuse" parts to him, it's sort of like he could attach a body builder's arm onto his mass and use it as though it was still alive, being super strong and such. Or if he somehow comes across a fire breathing dragon and takes the organ it uses to breath fire, and than he uses that organ to breath fire. It's easier for him to take over parts of a body rather than the whole thing, mostly because he doesn't plan on maintaining the upkeep of making sure that part of the body stays alive and well.

Edit:

Also, now that I've read through the other's CS's, I've noticed a certain lack of Villains. If you guys need it, I can make #27 into one. A sort of "Fallen Hero" type.