Tried getting a slime summon. So far he seems worse than useless, serving no purpose other than to use up mana and give the Alchemist Worshipper that I'm currently struggling with a way to get tactical advantage.
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When you get the Slime early on it is kinda cruddy (but still useful for the Darry+Barry fight), but as long as you've been feeding it, once you hit mid/late game it's stronger than Aura (excepting the fact that it has a Darkness weakness). It's Wind form is also practically a prerequisite for underwater combat. The Slime is also viable for the Alchemist when you get the Morph (Fire) skill at Slime Lvl 5. Note that the slime has to be unsummoned when you talk to the girl who taught you the summon spell, the game is not great about telling you this - I honestly got the Slime to lvl 7 before I figured that out on my first run because I practically always had the thing summoned.
One caveat with it being stronger though is that the Slime is definitely a lot better with the Bonding 1-3 passive (involves lewd scenes, will drop Victory Score).
... You can feed the slime? How? :o
EDIT: Figured it out. Huh, either I crit failed on reading comprehension a while back or the game did not explain at all that this mechanic existed. So I've gotten him to learn Protect I by feeding him Big Bones, but none of the other items I've tried have given him skills. What else besides Big Bones gives him useful abilities?
It's not about what you feed it, rather the Slime learns abilities at Lvl 2 and... 7, I think? My preferred strategy is to work primarily on MATK+HP via Living Hearts, Goblin Teeth, etc, (and whatever else is high value, though Avian Feathers can be a tough pick as Aura's AGI is a rather important stat). Also, 1 Mutant Spore will help with the Morph spells if you don't want to spend money on Mana Stones.
Once you get it later on, the Fire/Wind Slime morphs are arguably the best types to have it morphed into overall.