What: P.E.T., or "Pocketsize Extra Tiny" Aliens (there are a lot of acronyms in the world of mini figures, no?), a set of wacky-looking soft plastic aliens with painted details. According to MinifiguresXD there are around 30 different figures, but I only have the two pictured above.
When: Early-mid 1990s.
Where: Apparently these were mostly a U.K. thing, and were offered as cereal premiums there, but I remember getting the two I have as kid's meals premiums at White Castle here in the U.S. I am not sure exactly how many were offered that way.