How does Outpost of Tiranoc affect indirect damage from sources that dole out indirect damage to multiple players simultaneously, such as True Mage, Loremaster of Hoeth, Descendant of Indraugnir, and Moonstaff of Lileath? Does the dragon deal five indirect damage to each opponent, or does the High Elf player decide which opponent takes an additional indirect from the dragon and the other opponent(s) take the normal four?

Also, how does one Outpost of Tirinoc affect an attacking High Elf army of 1 Sea Guard Captain, 1 Spearhost of Asuryan, and 1 Descendant of Indraugnir with 1 Moonstaff of Lileath attached (and all three units are attacking). I guess it depends on if declaring attackers is one simultaneous event, or if attackers are declared one after another.

is it:

(A) All declaration of attackers is simultaneous and Outpost triggers once for 1+2+4+2+(1)=10 indirect damage to opponent

(B) Attackers are declared one by one, triggering Outpost three times for 1+(1)+2+(1)+4+(1)+2=12 indirect damage

© Outpost triggers for any indirect damage source, even if they happen simultaneously for the same trigger or one after another following one shared trigger for 1+(1)+2+(1)+4+(1)+2+(1)=13

(D) A, B, and C are wrong

Outpost of Tiranoc adds 1 to every instance of indirect damage. So in the case of Loremaster of Hoeth, with one Outpost in play, each player takes 3 damage.

In the "army" scenario, © is correct. With one Outpost in play, the Sea Guard Captain deals 2 damage to target opponent, the Spearhost another 3, the Descendant 5 to each opponent, and the Moon Staff 3 to each opponent. These are separate instances, so in a 2-player-game, the attacked player has to deal with these damages separately, he doesn't get dealt 2+3+5+3=13 indirect damage in one batch. So if he has a unit with Toughness 1, it can soak up one point from each instance, not just 1 of 13.