...I did that good of a job at hiding it? O_O Yay, I can do subtlety!
He's mewtwo in human form, basically. A very pretty, very attractive, glasses moe sporting human form. For all intents and purposes right now, though, he's human right down to his genetics with a few odd supernatural quirks.
The transformation between his two forms is kinda like Jack's Protean in a way, only Tom has only two transformations, his human form and his "true" form. He can also stay in either form indefinitely.
He can change back at forth at will, but pretty much the human one is the default for the moment, since it keeps the scientists away. It's also his
only form for any and all smut related activities. Because otherwise, ew. It's also his
weaker form. ...Be afraid.