Playing with my group the Return to Midnight Mask the other day, we came up with problem understanding the setup of the scenario. In the normal version of the scenario you spawn 3 acolytes. They have the forced effect to add one doom token to them when they enter the game, but comparing this effect to the one in their replacement, in Return to Night of the Zealot, the Disciple of Umordoth have the forced effect when they are spawned you have to choose to put one doom token on them or a clue on their location.
So we wonder, during setup who is "you" refered to. This problem came up because in a 4 player party, during the first mithos phase, we drawed Mask of Umordoth and then Masked Horrors , and all of us spended our first turn building up, and there wasnt an investigator with two clues on him/her to mitigate the Masked Horrors treachery card, thus the agenda 1 flipped over during the first mithos phase. Was pretty savage and we coudnt recover from that.
That was when we though that maybe the spawn effect of the Disciple of Umordoth was written so different than the Acolyte, and maybe they dont start with a doom token on them during setup.

We searched in the rulebooks for some clarification of the "you" part of the effect during setup, but didnt found a thing.

Can anyone explain to me how and why this enemy is spawned during setup?

Hi @Fenrirgarm

"You" can be a bit tricky, but it is covered here: https://arkhamdb.com/rules#You_Your under 'you/your' in the rules reference, and clarified in the FAQ here: https://images-cdn.fantasyflightgames.com/filer_public/12/ec/12ecf8b7-bd11-41f1-a243-155f607b3444/ahc_faq_v141.pdf at page 5, section 2.1.

In short, you refers to the person resolving the card most of the time. For spawning enemies during set up, the investigators may decide, and in the case of a stalemate, the lead investigator decides. (see Lead investigator: https://arkhamdb.com/rules#Lead_Investigator )