Primary: Early game units/cheap
examples: crawlers, swordwraths, bombers, etc.
Heavy: necessary meat shields for frontlines
examples: Speartons, Speardeads, Charrogs, etc.
Ranged: long ranged units
examples: Archidons, Eclipsors, Tdeads, Fire Elem, etc.
Support: Their main role is to support allies
Merics, Water Elem, Cycloid, etc.
Necromancer: They have multiple abilities
Magikills, Kais, Gorgons, Infernos, etc.
Hybrid: They are dangerous tanks in various occasions
Juggerknights, Giants, Atreyos, etc.
Assassins: They are good at taking down backline armies
Shadowraths, Rippriders, Crawlers, Shade, etc.