For people wanting to experiment and see all the various stages of the different mobs and such, perhaps adding in a Give Up button to expedite battles? Also, I can say for certain that at a certain size, you can't really lose to an enemy unless you just, sit there for several minutes. Makes it hard to grind up to have plenty of essence to give up to see all the different growth stages, and then actually be able to give that essence to various mobs.
Alternatively, perhaps an option to pay a given mob some essence to avoid a fight? Could have a fun bit of dialogue there, considering there isn't much when you lose a fight to one, and could also let you see them actually grow perhaps? Just some thinking on it, heh.
Also, the split runes are EXCEEDINGLY overpowered from my experience thus far, though I will admit I did gun for them specifically because they felt really powerful. You can just swarm your opponent with a metric butt ton of them if you get the right combination (somehow ended up with one that spawned one every tick and still was my highest damaging one) and it becomes a lot less of a frantic game of figuring out how to best use your stuff and more of a 'how many can I spam out per tick'. Pausing definitely makes it easier, I will say, heh, but still.