Monster Mash

Monster Mash is a PVP-enabled event quest in Fallout 76.

Quick walkthrough
Go to Watoga High School when the event is active. First player to get the monster mask is essentially marked "IT" for other players and enemies to attack and kill for the candy in the mask. The mask can be replenished by getting to candy buckets randomly spawned around the school, but guarded by charred feral ghouls. The quest lasts for three rounds. After the final round, the quest is completed. Successfully completing the quest for the first time awards the Monster Mash achievement. Halloween candy collected during the quest can be dropped off at the S.M.A.R.T. choice machine to be redeemed for either various junk, or other prizes of higher value.

Detailed walkthrough
When the quest starts, head over to Watoga High School. Once inside, the rules are explained: One player character needs to find the monster mask and put it on. Once they do, they are marked as "IT", allowing for other players and the charred feral ghouls in the school to attack them for the candy in the mask as during this quest, Pacifist Mode is disabled in order to attack the player wearing the monster mask. The longer the player character wearing the mask lasts, the more candy they earn for themselves. Candy buckets around the school can be collected to replenish the mask, but will be guarded in most cases by more charred feral ghouls. Once a player character wearing the mask is slain, the mask resets to another location in the school for another player character to collect to become "IT". After a round ends, player characters can deposit the Halloween candy they collected into the S.M.A.R.T. choice machine to redeem later for prizes when they've collected enough from doing the quest repeatedly. After three rounds of fighting each other and the charred feral ghouls, whoever collected the most candy wins, and those placed first, second, and third in the competition will be rewarded for their efforts with the quest completed. First time completing the quest awards the Monster Mash achievement.