Do you mean shapeshifting? It's definitely possible to shift into another character, humanoid or otherwise. I've stuck to the humanoid characters, for the most part.

Entering a dream as the character might be a bit trickier. I've had plenty of natural dreams where I'm thoroughly convinced that I'm a character from a TV show or a book or what have you. The trick is how to induce those dreams in the first place.

I try to program my dreams on occasion, and sometimes it actually works. The best way I've found of doing this is to daydream a scenario and write it down as if it's a real dream. Read over it a few times; keep daydreaming; read it before bed. With any luck, after a few nights you'll be dreaming your pre-programmed dream, probably with some minor adjustments.

As for WILDing... right. Anyone?