Sheer brilliance Maxdancona! They would make for an insane battlefield opponent!
This is what we have on the list right now:
The Mysterons from Captain Scarlet and the Mysterons (1967) as suggested by Izzythepush from a2k!
Xenomorphs from Alien (1979), etc....
The Yautja and the Hish-qu-Ten from Predator (1984), etc....
Terminators from The Terminator (1984), etc....
The Visitors from V: The Final Battle (1984 TV Mini-Series), etc....
Alien vampires from Lifeforce (1985)
Unknown 'critters' from Critters (1986)
The Borg from Star Trek: The Next Generation (1987)
Unknown alien force from Independence Day (1996)
Martians from Mars Attacks! (1996), etc....
Replicators from Stargate SG-1 (1997)
Arachnids from Starship Troopers (1997), etc....
The Scarran Empire from Farscape (1999), etc.... as suggested by oralloy from a2k!🐭
Psychlos from Battlefield Earth (2000)
Cylons, both Centurians and 'skinjobs' from Battlestar Galactica (2004), etc....
The Cybermen from Doctor Who (2005)
The Daleks from Doctor Who (2005) as suggested by Izzythepush from a2k!
The Weeping Angels from Doctor Who (2005) as suggested by maxdancona from a2k!
The Vogons from The Hitchhiker's Guide to the Galaxy (2005), etc.... as suggested by oralloy from a2k!
The Decepticons from Transformers (2007), etc....
Giant Kaiju from Pacific Rim (2013)
Malekith (Christopher Ecclestonand his army of enhanced warriors, the Kursed, from Thor: The Dark World (2013)
The Mimics from Edge of Tomorrow (2014)