3 months in a game, when I still had only laser tecnology and personal armors... and this is how I made my first acquaintance of Mutons (see attachment)
I defended the base with 20 soldiers and 1 tank. After an hour of meticulous shooting-and-retreating-tactics, 6 soldiers survived and killed off the aliens. One of the most challenging missions I ever did.
PS - This is superhuman in a "harder difficulty mod" that boosts the Mutons' armor and resistances to make them similar to TFTD's Lobstermen.