I used this guy in a fantasy campaign, he arrived in a ziggurat-shaped ship and mind-controlled some native tribes, who thought he was a god. You could also drop him right into the middle of the 17th century as well, what could go wrong.
Alien, Fairy, Demon
Armor 19, Move 120’, 6th Level Alien Grey
17hp, +3 melee 1d4+2, +3 uranium pistol 1d6+2, gamma cannon 6d6 save versus poison or roll mutation (Carcosa p.265), Morale 10.
Weird Spellcasting: 7 slots: Chaos, Wizard Eye, Duo-Dimension, Prismatic Wall, Gust of Wind, Shadow Monsters, False Alignment, Continual Light, Stone Shape.
Skills: Search 3.
Psionics: Mind Control, Telepathy 3/day.
Electronic Spellbook, 2 power cells, Battle Armor: AC 19, uranium pistol (300’, 100 charges), gamma radiation emitter (20 miles, 15 charges), +2 to hit and damage, can carry 900 pounds, force field 50hp.