“A cloaker is a shadow-dwelling, unearthly creature. They are normally only encountered in deep, dark caverns, far beneath the earth.” (Erol Otus, AD&D module A2: Secret of the Slavers Stockade by Harold Johnson with Tom Moldvay, TSR, 1981)
Ring-ding-ding-ding-dingeringeding, Wa-pa-pa-pa-pa-pa-pow. A party of Cynidiceans dances in frog, bird, and fox masks. "Cynidiceans are a special type of normal humans who live in the Lost City… They wear colorful masks, bright clothing, and carry short swords… They spend most of their time living in strange dream worlds.“ (Jim Holloway illustration from D&D module B4: The Lost City, written by Tom Moldvay, TSR, 1982.)
The Book of Foes, part of the Lords of Creation RPG by Tom Moldvay, cover by Dave Billman, Avalon Hill, 1983.
I like the idea here, though I would prefer a more medieval style illustration of the sci fi encounters. The possibility of a medieval artist trying to interpret an alien visitor reminds me a bit of the novel Baphomet’s Meteor by Pierre Barbet.