Level 1 (d14)
- 2d4 Acolytes
- d6 Bandits
- d6 Deep Ones or Subhumans
- Demon, Type I
- 2d4 Dimensional Sailors
- d6 Giant Ants (workers) or Giant Rats
- d12 Goblins or Kobolds
- d6 Hobgoblins or Gnolls
- d6 Lizardmen or Troglodytes
- d6 Orcs
- d20 Peasants
- Primeval Slime, 1 hd
- Serpent Man with d6 Subhuman servants
- d12 Skeletons
Level 2 (d20)
- d6 Bat Swarms (mundane)
- Bandit Hero with 2d6 Bandits
- d8 Berserkers
- d4 Cave Octopi
- d4 Colossal Leeches
- Demon, Type I
- Gargoyle
- Ghost
- d4 Ghouls
- d4 Giant Beetles
- d4 Hell Hounds
- d4 Hollow Men
- d6 Killer Bees
- Knight with 2d6 Men-At-Arms
- d4 Living Statues (crystal)
- d4 Man-Bats
- Primeval Slime, 2 hd
- d4 Serpent Men with 2d6 Subhumans
- d6 Shroommen
- d4 Vombis Leeches with d6 Vombis Zombies
Level 3 (d16)
- d4 Androids
- d6 Cave Crickets
- Cockatrice
- Demon, Type I
- Friar with 2d6 Acolytes
- d6 Giant Ants (soldier)
- d6 Giant Centipedes
- d4 Giant Cobras
- d4 Living Statues (stone)
- Lizard, Giant
- Magician with d6 Peasants
- d4 Owlbears
- Primeval Slime, 3 hd
- d4 Underdark Slugs
- Witch with d6 Servitors
- d12 Zombies
Level 4 (d10)
- d4 Bat Swarms, vampiric
- d6 Bugbears
- Demon, Type I or II
- d6 Insect Swarms
- d4 Living Statues (Iron)
- d4 Ogres
- Primeval Slime, 4 hd
- d6 Rat Swarms
- d4 Giant Vipers
- d4 Time Travellers
Level 5 (d16)
- Ape-Man (Giant or Four-Armed)
- Basilisk
- Brain Elder
- Chimera
- Cyclops or Giant
- Demon, Type I - VI
- Elemental
- d4 Giant Scorpions or Giant Boa Constrictors
- d4 Harpies
- Hydra
- Manticore
- Minotaur
- d4 Mummies
- Primeval Slime, 5 hd
- d4 Shadows
- d4 Trolls
Notes:
I put Peasants on the first level chart under the assumption that the party could run into an NPC funnel group.
Given how often they come up, the GM should probably pre-generate some Type I Demons and Primeval Slimes.
Level 4 is kind of boring, isn't it? It's like the calm before the storm of getting completely clobbered on Level 5.