"The Thousand Young" card states that each Investigator must immediately begin combat with a Dark Young. Must the Horror check be passed first?

If the card reads "must pass a combat check against a Dark Young", then, no. If the card reads "begin combat" then yes, the Horror test is the first step of the combat sequence if you choose not to evade the monster

If the card reads "must pass a combat check against a Dark Young", then, no. If the card reads "begin combat" then yes, the Horror test is the first step of the combat sequence if you choose not to evade the monster

Since the wording here is "begins combat', then, according to your explanation, the first step of this combat sequence would be the Horror test. Evading the Dark Young is specifically forbidden by this Sinister Plot.

I also have one related question. Shub's normal Attack involves passing a "Sneak" check ---- it starts off at +1 and the check's modifier diminishes by 1 each turn thereafter. On the AO card, the following examples are given: +0 the 2nd turn, -1 the 3rd turn, etc.

Is the draw of this Sinister Plot (which utilizes a special Attack by the Dark Young) considered a "turn" as far as Shub's normal Attack is concerned? To be more specific, "The Thousand Young" Sinister Plot was drawn on Turn 2 of the Final Battle. Would the "Sneak" modifier on Turn 3 be -1 (as stated above) or 0 (because the 0 modifier had not yet been done)? Thanks Julia for your on-going assistance.

I think (beware, I think, it's something like 4 years since I played Shub and I never went to final battle with her) that the two things are separate, i.e. you count the number of rounds of final battle to determine the modifier (so, in your example, turn 3 is a -1). I'm saying this because this is the way it works even if you use an attack canceller of some sort. Let's say you use an item cancelling the first attack of Shub; then when you go the next round for her attack, is a +0, not a +1

1. Yes, combat in this case includes a horror check. It's as though you're encountering the Dark Young (minus the ability to evade or flee). Note that the +1 toughness from Shub still applies, as all "slumber" abilities are still active in final combat.

2. Yes, every turn in final combat, whether you're allowed to attack Shub, still counts towards toughening her defense modifier.

1. Yes, combat in this case includes a horror check. It's as though you're encountering the Dark Young (minus the ability to evade or flee). Note that the +1 toughness from Shub still applies, as all "slumber" abilities are still active in final combat.

2. Yes, every turn in final combat, whether you're allowed to attack Shub, still counts towards toughening her defense modifier.

Thanks Tibs. I didn't realize that all slumber abilities are still active after the AO wakes up to do Final Battle. Ultimately, it didn't matter because my 4 Investigators did not survive the Epic Battle.