Before asking this question, I opened a Meta discussion to check if it's legal here. The question is about Pen&Paper, not video game rules.
In Vampire: the Masquerade — Bloodlines, Sebastian LaCroix is a local prince who uses Dominate•• several times. At the end, LaCroix tries to use Dominate on the game's protagonist twice in row and fails, but no diablerie took place.
How could I have a vampire that could resist Dominate•• like this in the pen & paper game rules?
This is what the Iron Will Merit is for.
From V20:
Iron Will (3pt. Merit)
When you are determined and your mind is set, nothing can thwart you from your goals. Characters using Dementation, Dominate, or any other mind-altering magic, spell, or Thaumaturgy path against your character are at +3 difficulty.
Elder levels of powers like Dementation and Dominate may overwhelm even this resistance. Against Level Six powers, the expenditure of a Willpower point through Iron Will only raises the difficulty of the Discipline roll by two. Against Level Seven powers, the difficulty is increased by only one. Level Eight and higher powers cannot be resisted with Iron Will.
This Merit does not affect Presence or other powers dealing with the emotions. Characters will Willpower scores below 8 cannot take this Merit.
And from Revised Edition (The edition of record when the game is made):
IRON WILL (3-PT.MERIT)
When you are determined and your mind is set, nothing can thwart you from your goals. When you are affected by a Dominate power, you may spend a point of Willpower to shake off the effects. In addition, you receive three extra dice to resist the effects of any mind-altering magic, spell or Thaumaturgy path. This Merit does not affect Presence or other powers dealing with the emotions.
My guesses are that the only real option could be that LaCroix just failed/botched both rolls. I don't remember any Discipline that allows to actively resist Dominate.
Tremere protagonist could use Blood of Potency (Thatumaturgy •••, Path of Blood, the one the protagonist has) to buff Generation to lower than that of LaCroix.
Willpower of the protagonist is not shown. It might be possible that the protagonist just developed it to an amazingly high level, so Dominate just became a joke for him/her, and Iron Will Merit could be developed during the story at Storyteller's description, or present from the beginning.
