Sorry, but if I'm at level 1 and need to 50 something exp for the level up from 1 to 2 and the only enemy I can fight are either the not beatable students or the rats, which give just 1 exp each, how is that not grinding? I needed to kill at least 50 rats to get to level 2, which is grinding. And starting my safe, that worked just fine until this version, and still does, except for the skillpoints and skill, and seeing that I have -2 skillpoints, that's also not really cool. This meant for me, I needed to at least get to level 4 for 1 new skillpoint (luckily when I got to level 3, I was at +1 skillpoints, don't know why). Until I stopped playing, because the only content left, that I could unlock were the fairies, I could only fight and beat rats. There was no main story left. So please explain, how that is not grinding? Are there weak enemies other than the rats? If so, please tell me, where to find them.
You get enough skillpoints from story and don't even need to lvl up to win most fights. But let's say you want to...
The weakest rats give 1 xp. The stronger versions give 2 and 3 respectively. Reaching the plague girl should get you lvl 2-3 without pointless grinding, literally just going in a straight line to the boss. Side rooms have some optional content, items and rats if you really wanna get that extra XP for an additional lvl, but it's optional.
Now, keep in mind you don't even have to lvl up. You just need the right skills, even for mages. The skill system is based off guild wars1, where you're meant to adjust your build and skills to the situation.
Rats, mana shield & fire ground. Two skills is all that's needed. You can grab some undead skeletons and demons and spam 'all minions attack' if you prefer.
Mages, grab invisibility and something that kills their mana. Mana shield would be helpfull too if you get hit.
There's also the 4 monsters in the arena, but they also need merely adjusting your skills. Manticore best grab some rat talismans for tanking. Golem might be the only problem for you.
As for the fairies, if you really see no other way, cast invisibility on yourself and your demon before combat. Summon two skeletons or some rats. Wait for the fairies to drain their mana on your summons while your hero watches. Five rounds later you simply kill them off. Remember to grab some potions and equip some items for extra dfn/atk.
If you still struggle with something, let me know.
EDIT: Double checked your post... Your skillpoints are on minus most likely due to learning undead spells. Learning these did not initially consume skillpoints due to a bug. You can unlearn them if you wanna.