how can you get it make a stopmotion character to ineract with a live character?

Question

you know because im really good at stopmotion animation and i want it to look like the stopmotion character is with the living character

Answer 1

What you're describing is Chromakey (the "blue screen" process)...your animated character and your actor(s) should be filmed separately (the character being filmed in front of a plain color background).

You can do your own version of Chromakey by using that lime-green posterboard as a backdrop and then using Adobe Photoshop (or something similar) to eliminate the BG from the image and then merging that with the live action footage. I'm just giving you an idea to start on,so you might want to do further research on this.