Low:
1 - Goomba
2 - Grunt
3 - Infected
4 - Zergling
5 - Tarkata

Middle:
1 - Locust
2 - Wraith
3 - Splicer
4 - Helgahn Trooper
5 - Reaper

High:
1 - Behemoth
2 - Big Daddy
3 - Spartan
4 - Jedi
5 - Collossus


This is my preferred order as well.

1.  Goomba
2.  Grunt
3.  Zergling
4. Boomer
5. Headcrab

6. Splicer
7.  Locust
8. Helghan Troop
9. Koopaling
10. Reaper

11. Behemoth
12. Big Daddy
13. Jedi
14. Spartan
15. Colossus

Low:
1 - Goomba
2 - Head Crab
3 - Grunt
4 - Zergling
5 - Boomer

Middle:
1 - Splicer
2 - Wraith
3 - Koopaling
4 - Reaper
5 - Undead

High:
1 - Spartan
2 - Big Daddy
3 - Behemoth
4 - Jedi
5 - Collossus

Low:
1 - Goomba (Mario)
2 - Ghost (Pac-Man)
3 - Raider (Fallout)
4 - Head Crab (Half-Life)
5 - Grunt (Halo)

Middle:
1 - Splicer (Bioshock)
2 - Undead (Dark Souls)
3 - Reaper (Mass Effect)
4 - Darkspawn (Dragon Age)
5 - Hunter (Left 4 Dead)

High:
1 - Behemoth (Fallout)
2 - Colossus (Shadow of the Colossus)
3 - Spartan (Halo)
4 - Jedi (Star Wars)
5 - Big Daddy (Bioshock)

1-Goomba
2-Ghost
3-Skeleton
4-Infected
5-Headcrab

6-Undead
7-Hunter
8-Splicer
9-Helghan Trooper
10-Locust

11-Spartan
12-Big Daddy
13-Behemoth
14-Jedi
15-Colossus

If I may, I would like to throw Black Phantom into the ring for high tier

Didn't thoroughly read. Re-doing.

I'd like to request a few more additions, because I feel like there aren't enough franchises included. I also would like to request that each series only be representable once (so none of this "oh hey, let's put Halo and Fallout into the running twice!" crap).

Other additions:

Low ranks:
-Deku Scrub (Zelda)
-Metroid (Metroid)

Middle Ranks:
-Herobrine (Minecraft)

High Ranks:
-Nemesis (Resident Evil)
-Tyrant (Resident Evil)