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Well, regarding the UNIQUE skill.
Here's a draft with all the options I could come up with, and some of the ones suggested in the thread.
+2 skills / +1 perk;
+20 HP, +2 accuracy, reaction, speed, +3 willpower;
Immunity to injuries and negative effects;
The character always goes first, regardless of their own initiative;
The character learns new things (from books or other characters) twice/three times faster during time skips;
Representatives of various and illegal organizations are more willing to ally with the group / bonus to reputation;
Positive effects applied to the character (/by the character) are twice as effective and do not dissipate until the end of the battle;
Health +15%, passive health regeneration 15% per turn;
Enhanced version of any skill or spell known to the character;
+15% critical hit;
2 spells per turn, +2 attacks for one-handed weapons, bows, polearms, +1 attack for crossbows, two-handed weapons;
The chance to inflict any negative effect on the target, whether it be paralysis or disarm, is twice as high;
Further, more options for me, as the leader, because we might not be able to complete all five quests:
Antimagic Dome (active skill). The character places a barrier in the selected area that instantly dispels all magical effects and prevents the use of magic within its boundaries;
Inspiration (active skill, once per battle). For the next turn, all allied attacks will guaranteed hit the target / for the next turn, all allies will survive fatal wounds / dispels all negative effects applied to allies;
Inspiring Aura (aura). Allies around the character receive bonuses to willpower, accuracy, and reaction / speed, ignoring the heavy armor restriction;
Annihilation. Deals 10 units of pure energy damage to the selected opponent, bypassing all checks, shields, and resistances;
The numbers are just estimates, I didn't put much effort into them. You can take a look and choose, or suggest something else, or I'll choose from this draft later, after consulting with Revan about the numbers, something like that.