This is a rather unusual & rare item! It's the Sonic Badge & Magnet Moulding Set. It's a kit where you can make plaster shapes & then paint them with the enclosed colors. If you glue a magnet to the back, it can go on the fridge. Glue on a pin-backing & pin it anywhere (a badge). The stock Sonic has had a random pair of sunglasses just sort of pasted on there for some reason.

You can see all the designs it makes on the front. (That's Katerkiller behind Sonic's head) You can make 3 Sonics, 2 Tails', 1 Robotnick & several badniks including chopper fish, katerkiller, crabmeat & maybe kekleon. The likenesses are just ok. With the 2nd photo you can see what was included, like plaster bucket, plaster pack, stirrer & measuring spoon. This was available at Waddingtons stores in the UK area at some point in the 1990s. Plaster pins are somewhat impractical, as plaster is easy to chip or crack. However, they'd do well as a magnet. This kit is a fun idea for kids projects.