I love cards which step out of the main line, and sacrifice is wonderful in this category, and I agree she does seriously need help !
TL:DR -> What about :
- Her main spell should NOT kill a unit.
- Her main spall should continue to boost magic and only magic
- Her main spell should scale with Disease (or web, or poison) instead of Death marks
- Her third trait shall do something when an allies dies
This way, sacrifice would greatly benefit teams with Boombots, Black Beast, Sacrificial Priest, the Princess of Silverglade, as well as team using summons as cannonfoders.
Could use with Dolfakkar (summon and use magic for damage), or Venbarak (mass disease, magic scaling aoe damage), ...
Why sacrifice = magic boost ?
Justice is offensive life/attack boost (blue loop).
Courage is offensive life/attack boost (skull spams).
Humility sounds like a well-rounder, but is mostly used for magic buff in loop teams (pray for that +magic to land on your aoe guy).
Loyalty and Honor (needs buff) spells like defensive.
And purple color is color of pure magic.
So it feels logical that sacrifice shall remain a magic buffer.
Why not death marks ?
First the debuff is hard to apply : few troops use it, most apply it on a single target (by spell : succubus, or by skulls:wraith, herald).
Second, half the troops applying death marks don't scale with magic or in a non efficient way (i.e. boost a random stat or give souls). (Penitent)
Death being the exception here (4 marks, magic scaling damage), but it's a Mythic.
While I agree death marks resounds with sacrifice (own death), I feel it's more beneficial for the game (gameplay wise) to scale with disease, web or poison.
Why stop killing one's ally ?
We already have a few troops which core mecanics do kill an ally : black beast, sacrificial priest, that silverglade princess, and they are already quite hard to use due to the sacrifice of going down to 3 for "some" benefit.
I thought it would make more sense to have Sacrifice encourages sacrifying troops instead of killing them himself. In addition, she would find ways in non-sacrificial teams, especially teams summoning weak troops to get skull-crushed by the opponent.
However, Black beast and Princess Elsphet do not scale with magic