Right next to Vecna he says, "You were brave the first time. But let's see you get frightened now!" 

Frightful Presence (eh, it's a free action so why not?)

Bite: Attack: 35 Damage: 18
Claw: Attack: 26 Damage: 17
Claw: 31 Damage: 20

He then moves another 80ft up (now at the height of the 200ft ceiling I believe.)

Note to self: Bite, Claw, and Tail have some reach. You don't need to go right next to the enemy.

Vecna flies 60 feet straight up and teleports next to the dragon. They take 10 psychic damage and Vecna regains 80 hitpoints.

I use rotten fate again.

DC 22 or take 79 necrotic damage or half on a success.

then he makes two attacks with afterthought.

to hit: 19 damage: 9 piercing plus 10 necrotic. If it hits, make a DC 20 con save at the start of each of your turns, taking 9 necrotic damage on a fail. This effect lasts every turn until you make the save.

to hit: 22 damage: 9 piercing plus 11 necrotic. If it hits, make a DC 20 con save at the start of each of your turns, taking 13 necrotic damage on a fail. This effect lasts every turn until you make the save.

Fly requires concentration. So I believe he would have to make those concentration saves first.

Oh yeah. 3 of them, right?

30

20

29

Believe you made them all.

Rotten CON Save: 32 or 24

first afterthought is a miss

Second Afterthought CON Save: 28 or 28

Legendary Action: Wing Attack

DC Dex Save throw or take 22 bludgeoning and get knocked prone (I don't think fly mentions a hover)

that's a *DC 25 DEX Save (don't want to mess up the rolls)

and breath recharge: 5

385HP

Lair Action: glimpse into future

normal turn actions: TODO

[[and I think I'm gonna call it a night at this point, gonna cut up brownies and head to bed]]

Dex save is autofail, I fall 200 feet and take 74 bludgeoning.

Quote from VitusW >>

[[and I think I'm gonna call it a night at this point, gonna cut up brownies and head to bed]]

 *alright, good night!*

[[sorry about putting this off for a while]]

I believe I still needed to get the dragon's normal turn going.

Let's see about fire-breath recharge. 4

Alright. So with that the dragon (385hp) will fly down 70ft (130ft from Vecna) and await the liche's actions.

And Vecna is at 198hp, right?

I believe.

Vecna will prepare to use rotten fate if the dragon flies within 120 ft of him.

5 on recharge

Quote from VitusW >>

5 on recharge

The gold dragon swoops down, bearing the brunt of Vecna's rotten fate as he goes down 40ft to unleash his breath at the liche.

Con save: 17 or 35

Breath: 80 fire damage DEX Save DC 24

After making the swoop he returns up into the sky. (40ft up to prior location)

Quote from VitusW >>

Quote from VitusW >>

5 on recharge

The gold dragon swoops down, bearing the brunt of Vecna's rotten fate as he goes down 40ft to unleash his breath at the liche.

Con save: 17 or 35

Breath: 80 fire damage DEX Save DC 24

After making the swoop he returns up into the sky. (40ft up to prior location)

 so half damage on the rotten fate

Rotten fate: 97

dex save: autofail.

Vecna flies 60 feet up, teleports 30 feet more, and casts dominate monster.

So Vecna is 40ft from dragon.

Wis Save; 17 or 13

The dragon, failing the wisdom save, uses one Legendary Resistance to succeed instead. 

Legendary Action: Wing Attack (Vecna out of range) then moves half its speed. Now 170ft up and 80ft from Vecna.

Breath Recharge: 2

The dragon, seeking to get distance, moves 30ft up at an angle and then 130ft to the side (dash)

in retrospect, should've done some side-angle on the previous probably

Question: For the multi-attack feature of a creature, do you know how things like shove/grapple/etc go? Replace one attack from the multiattack with it or is it the whole that gets replaced?