if you target player X 3 times with vigilanteism and then target player Y with duel, it will repeat the last effect from vigilanteism (which would be cold steel)
since you’d only have targeted player Y once, you’d do the second part of cold steel as opposed to murdering them
the assassin can choose from those effects every night and it’s not an ability so it doesnt say (infinite uses) – i guess it could be worded differently such as
Bypasses healing - 2 uses, even night
Bypasses death immunity - 1 use
You will not be seen visiting your target - infinite uses
Their flip will be cleaned - 1 use
Roleblocks the target. Additionally, if they survive, they will be unable to use any abilities for the rest of the game (unless they are Neutral/Unshackled) <insert the clarification that this is removed if they are converted, somehow> - infinite uses
in which case i guess you can yell at geyde or datbird