Holy Canoli...
Can you still merge spirits after they're maxed out? Is there a stat ceiling that all monsters can reach or do you have to plan and pray?
You can raise a monsters level if you merge it with the same type of monster at max level:
Werewolf LvL 1 + Werewolf Lv1+ Werewolf LvL 1 + Werewolf Lv1+ Werewolf LvL 1 + Werewolf Lv1+ Werewolf LvL 1 + Werewolf Lv1+ Werewolf LvL 1 + Werewolf Lv1+ Werewolf LvL 1 + Werewolf Lv1+ Werewolf LvL 1 + Werewolf Lv1+ = SuperWerewolf Lvl 15
SuperWerewolf Lvl15 (Max Level) + Werewolf Lvl 1 = SuperWereWolf Lvl 15 (Not max level)
And you can only raise the level cap once for common, twice for uncommon, three times for rares and 4 times for super rares.