How did you come up with 4?
Mafia eats 1 person.
SK eats 1 person.
Vigilante can eat 1 person. (More than likely wouldn't happen)
That makes 3.
The best case would be 1 death.
Mafia attempts to eat the SK but fails.
SK eats 1 person.
Vigilante goes vegetarian.
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The only information we get is from the Lynch. The Cannibal mechanic has no effect on lynches.
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Ok, if you include the Lynch, then it's 4 deaths.