His math is not off (you can't just declare math is off without showing the math is off)
It is off (slightly) because of his assumption about using Lucky and that he adds full 14 damage for arcane shot (instead of multiplying it by the 0.55 hit probability). The DPR is closer to 129-130, his was too high. Regardless, the point stands that such damage would be close to defeating Vecna by two fighters, and with a bit of good damage rolls, would defeat him.
So going back to the Monk/Pillar thing....I am genuinely confused as to why the monk felt he needed to attack the pillar in the first place....was it to get a flurry attack against Vecna without triggering his reaction on the first attack?
Yes. That is why I did it. People have claimed it is a bit cheesy (which it is LOL), but it is no different than if a skeleton or zombie minion was next to Vecna and I had the monk hit the minion to activate Flurry first before using it on Vecna.
Also, in doing some more rule research after the fact I posted how it was something I didn't even need to do: he could have grappled Vecna without triggering Fell Rebuke (which requires a "hit" and grappling is not a hit). In the same respect, Leon in round one, post #162, (who grappled Vecna) would have been able to attack to smite since Venca
should not have used Fell Rebuke then, either. So, that was my error in not realizing a grapple is not a hit.
Depending on how you want to rule the attack requirement of Flurry of Blows, you get a couple variants here as well.
1. Grapple (Attack), Flurry, Flurry, Strike (Extra Attack)
You have taken the attack action, so my use Flurry prior to finishing the attack action.
2. Grapple (Attack), Knock Prone (Extra Attack), Flurry, Flurry.
You must complete attack action, including Extra Attack, prior to Flurry.
From what I have found, JC rules along with option 2, although I would DM option 1 is fine. Regardless, it all works out to the same result in the end: Vecna -- grappled, prone, and no reactions until the end of Hjalman's next turn.
I do feel bad reading the last 3 pages and its nothing but commentary as opposed to the actual simulation.
I am waiting on others to chime in on ruling whether or not Leon's Improved Divine Smite will work in the Antimagic Field... I asked for others to give their views, and nothing on that.
Sage Advice is IDS should work, but that means he can make melee weapon attacks (as "magical" enough???) to deal damage to Vecna... I think?