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.
What's it worth? Take a look at this Strange Change Machine price guide: sold listings for a value indication.