For all help and discussion relating to visual effects in programs that are not already covered in an existing forum, such as Blender, Particle Illusion, etc., along with discussion about effects theories and techniques.
Okay... you talking about having two characters from two different shows on top of the same background? If so just mask them out using Photoshop, Vegas, or After Effects (Photoshop being the best. Even the "elements" series allows some basic masking.)
Just take the scenes you want to have the character cut out of and erase everything else to transparent.