For those of you who care about Monstrosity or are interested how I leveled Slime (eventually Boil):
1) Equip HP / DEF / Store (or even better conserve) TP instincts.
2) Go to zone and put up defensive spells / abilities
3) Pull enemies with stone (Boil is PLD/DRK)
4) At 1,500 TP use Cytokinesis. Does about 800~1,600 damage to every enemy around you.
Amazing fast way to clear the 500+ damage RoE. I got about 50 or 60 uses in that RoE each pull.