First of all thanks a lot for your explanations and great suggestions. I already realized a lot of mistakes I have made and I am not sure how long it would have taken to realize it on my own.
So I bought the respec necklace to correct some of my errors and made a new party:
My main (mage), Cassandra (tank), Sera and Cole.
I did so because i wanted to combine Mark of Death with Thousand Cuts as well as Rally and Mark of the Rift.
I tried to fight the The Highland Ravager and my best result was bringing it down to 30% hp. (it is still frustrating to have to use ~10 seconds of battletime to revive somebody but from what you have written here I think it should also work for me by now)
After the fight I've read somewhere that I should have at least level 23 for trying that dragon. Before I followed your suggestions I wasn't able to even come close to this result.
Can you please tell me if you see any bad mistakes from the list of my abilities I unlocked?
What I did:
Mage: (everything except dispel is disabled so I can take full control)
Barrier
Dispel
Chain Lightning
Static Cage
Winter's Grasp
Flashfire
Stonefist
Mark of the Rift
Actually I have upgraded all the spells I'm using. The reason I have left Flashfire in there for my fight against a fire-dragon is that I don't have another usable skill to replace it anyway (yet). I focused on passives:
Peaceful Aura
Guardian Spirit
Stormbringer
Gathering Storm
Flashpoint
Clean Burn
Mana Surge
Do you think Firestorm is good against ice-dragons? (better than Mark of the Rift?)
Actually I'd like to unlock Static Charge next. This will take 2 more levels for me.
Cassandra:
War Cry (preferred)
Unbowed (preferred)
Challenge
Charging Bull (preferred)
Shield Wall
Shield Bash
Blessed Blades (disabled)
Rally (disabled)
All upgraded too.
First I wanted to use Wrath of the Heaven too but I decided to use Shield Bash as it is better against block.
Passives:
Bear Mauls the Wolves
Untouchable Defense
It'll cost you
Trust the Steel
Cutting Words
Maker's Will
There is no Darkness
Sera:
Abilities:
Flank Attack
Deathblow
Twin Fangs
Hook and Tackle
Flask of Frost
Stealth
Thousand Cuts (disabled)
Passives:
Dance of Death
Sneak Attack
Looked like it Hurt
Evasion
Easy to Miss
Flaskmaster
(I know I should unlock Pincushion... but not enough skillpoints yet)
Cole:
Abilities:
Flank Attack
Mark of Death (disabled)
Deathblow
Stealth (preferred)
Knockout Powder
Poisoned Weapons
Hidden Blades (disabled to save it for Mark of Death)
Cloak of Shadows (disabled) (I think I'm gonna exchange that one later - I haven't found any good use for it)
It is embarassing but I forgot to exchange Cassandra's Serpent's Rage. Still.. after using the 'new' abilities she did not die during my fights.
Sera and Cole have quite similar stats. (no new armor here)
...and I used the Fire Resistance Tonic for Cassandra and Sera. Cole used an attack tonic but I will change this to a resistance tonic on the next run (against another dragon).
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edit: I was able to bring Kaltenzahn down to about 30.000 hp and lost the battle because I had to waste 5 healing potions because my characters continuously interrupted any try of reviving. All together I wasted about 20 - 30 seconds of battle time to keep my characters from running away from reviving. On all my 3 tries.
Actually I have no idea how others were able to handle these experiences. ^^