EASY WAY TO REMEMBER:

TIER 1 (After REX/WEEVIL)
Sogen/Forest/Yami/Wasteland
Insects
Reptiles
Beast-Warriors
Fiends

TIER 2 (WEEVIL/MAI)
Little Dinosaurs (not Uraby or THKR)
Fairies
Fish
Waters
Spellcasters

TIER 3 (MAI/KEITH)
Winged Beasts
Fake beasts
Warriors
Uraby/THKR
Machines

TIER 4 (ISIS)
Zombies
Plants
Females (Warrior/Fairy)