The Thingmaker was the device that used the Plastigoop! It was essentially a little electric skillet just big enough to hold the molds that came with it. You poured the Plastigoop into the molds and baked it until it hardened. The final consistency was rather rubbery (unless of course you burned it.) I had one of the first versions of this toy and the molds were for bugs, worms, spiders, etc., thus the name Thingmaker.
Later versions came out with flowers, GI Joes & accessories, etc. The Plastigoop colors went from 4 basic colors to a huge variety - pastels, glow-in-the-dark, etc. I think there were glittery colors, but won’t swear to that.
My brother had the GI Joe set and you put wires in the liquid plastic before cooking so that the end product could be posed.
I know my sibs & I had other sets besides the 3 I named, but these are the ones I remember.
Oh yeah, the name of the first set was Creepy Crawlers.
Just Googled it. Wow! The choices they have today!
http://www.snowcrest.net/fox/thing.html
http://www.snowcrest.net/fox/goop.html
Brings back memories. The Creeple Peeple were really cool!