god tier

archer
outcast
alchemist
mermaid
halfbreed
yggdrasil
yung witch doctor
lord of death
sea giant

high tier

flying machine (only for ranged dps stacks)
disciple
aqua spirit
nightmare
overseer (stacks with upgrade)
bone warrior - 1st 2 upgrades early
ice troll (stacks with upgrade)
neotank
infantry - early
dark priest - late, god tier w/ disciple
prisoner - early
orc warrior
ghoul - early
steam roller
druid
goblin scientist
orc warlock

mid tier

seer of darkness (high tier w/ disciple)
ent - early
mudman - early
carrion spitter - early
ranger - early
tree of travel
ogre basher - early
harpy
troll fighter
grizzly
priest
knight
dragon hawk
bottom feeder - early-mid
hatchling
machine turret - early
captain - late support stacking aura
tempest - early DON'T UPGRADE
necromancer - upgrades for each phase of game
acolyte - early
tribesman - early
medicine man
moon guard - early
polar bear
wandigoo
yung drost dragon - early-mid
specter
wanderer - upgrade to hero good early tank, villain shreds armor
phantom - early-mid
apparition (stacks with upgrade)
frost wolf - early
sentry - early
novice - upgrades good early
cyborg
minotaur

low tier

sprite
watcher
spawn of dragon
knoll warrior - AS debuff, only use if you don't already have one
footman - early
komodo
egg sack
geomancer - early
zombie
guardian of death
servant
harlot
wyvern
orc warchief

shit tier

peewee
peasant
proton
land mine
tuskar
gate gaurd
colt
raider
meat wagon