I've been wondering, is there some level where you stop getting skills? I'm level 40 now and haven't been offered skills for awhile. In the mind tree, I only have 8 skills.

You can still get skills until the end, but chances are getting lower and lower though. If you don't get skills at all in further levels let me know.

when you don t get any skill just reload the last fight when leveling up .

Yeah, but that is kind of cheating... we couldn't avoid that possibility of reloading... still with no skills there are other options to get.

Any tips for the beginning of the game, when I don't have mana or troops but am supposed to beat the undead? I can sneak in the castle and buy eg. one Marauder, but that doesn't help much against a Black Knight. And I am supposed to have annihilated all undead if I reach the castle.

Talk to Runolv, there are option in dialog to choose some attack spells that help to beat undead behind gate. First as you say sneak to castle, after talk you get experience close to the 2-d level; after the first battle you get the 2-d level, try to choose nice skill, for example berserker.

Or buy damage/healing spells. Sometimes you can buy level 1 creatures at the Smith or at Runolv too. You always get Cave Spiders from one of the 2 trees in front of Runolv, and Cave Spiders have the ability to cast Mass Web once in battle. It webs 3 random units including your own. That can sometimes help.

In an earlier testgame we had placed the 50 leadership flag near the castle, it looked like part of the scenario, and the tester couldn't find it, and you have zero leadership from the start... so we moved the flag to the starting position.
Early skills I would choose something that gives Mana or Rage unless something like Concentration or other good skills comes up. There are now 2 skills in the Warrior tree that gives eather Mana or Rage, the old Attack and Defense skills gives up to 10 Mana or Rage. The Defense skill has changed name to Fortify (gives Mana and Defense). Still Onslaught, Rage Control gives Rage, Meditation/Wisdom/Artifactor gives Mana.

BTW some creatures can give skills too in troop talk after a fight. If you carry one of these (can be in the Reserve too):
Berserker: Can give the Berserker Skill !
Chaos Dragon: 50% chance of getting the Chaos Magic Skill
Slinger: Gives Quick Draw Skill
Orc units can give extra Rage
Druid can give Mana (as far as I remember), and change into Soothsayers.
etc etc.

You get the skills even though you don't level up, it is Acrimaldo that teaches you after a fight.

Any place I can get a list of what creatures have what?
I currently have hunters, avengers, pyromages, paladins, and rune mages. I carry a stack of satrys in reserve solely to get the troop talk benefit from them (+10% mana pool). There's a lot of troops I haven't experimented with yet.

We haven't posted a list yet... there're so many... so don't think we will be doing it, could also be players posting .
Anyway it is only level 1-3 that gives bonus from troop talk. I wrote some examples in earlier posts.

dryads can be transformed to ice nymph

p.s. what impact on power of books of nightmares? I have 18 books and they do so little damage comparing to my 9 book of evil?