The Strange Change Machine was basically a two-way conversion device, built to resemble a quasi-futuristic time-machine thingy. Its base was old-fashioned, solid metal, painted a saucy crimson; at its top was a plastic see-through dome. It came with a series of differently-colored little vinyl squares ('time capsules'), a printed map of a prehistoric jungle land, a set of plastic mountains to give the map some depth, and a pair of tongs. The tongs were absolutely necessary.
The premise of the toy was that the cubes were actually monsters, which were hibernating in the Starburst-like forms, waiting to be unleashed by the mad scientist (the child). The cubes were placed inside the see-through plastic chamber, where they were heated; and the cubes, consisting of 'memory plastic,' would revert to their original shapes - a variety of weird-looking monsters and dinosaurs. They could be removed from the heat (using the tongs) and, after cooling, could be played with normally, as little plastic figures.
If they misbehaved, the child could turn them back into cubes by reheating them in the chamber (remember to use the tongs!), and then placing them inside a small metal chamber in the toy's base, where a hand-cranked vice would take the now-softened monsters and squish them back into cube form - complete with the Mattel logo on one side.
The Strange Change Machine was one of several similarly-themed toys in which children messed around with molten plastic and such. The Thingmaker was a popular line where kids poured variously-colored plastic goop into a mold, creating their own bugs, characters, etc.; and the earlier Vac-U-Form machines allowed kids to created their own small plastic toys through a common industrial method, shrunken to fit their little needs.
As a kid, I never owned a Strange Change Machine - they were a little before my time - but I had access to one when I visited relatives, several times a year, thanks to an older cousin who had outgrown his toys and put them away for a while. There were no instructions, so I had to figure out what the heat and the vice were supposed to do. It was a nice toy for a young boy - especially a kid who was fascinated by monsters, lost lands, and time travel. Many of the monsters were pretty cool: my favorite was a sort of mothman, with melty-looking wings (he can be seen in the accompanying box photo).
Alas, Mattel only produced the toy for a short time, probably owing to the fact that so many kids were scorching themselves on the hot plastic pieces (or on the metal grill at the bottom of the dome structure), or else were crushing their little brothers' fingers in the compression chamber in an attempt to extort lunch money.