Pepin creates his force ballista and puts it on his shoulder while he drinks the flying potion, thinking it will be usefull this time around. Although, for now, he stays on top of the main gate. Finally, as soon as the wyverns are within 300ft he casts Ice storm in the middle to target as many of them as possible. (20ft radius, 40ft high column)
DC21 dex save or take 30 damage (12 bludgeoning, 18 cold); half on success.

Tempe summons Pinky, then polymorphs Pinky into a giant eagle, riding him, he goes to intercept the riders. "Hold my friends, lets see what they want, first."  

Zenodor finds himself a nice lookout to snipe from. If necessary, he will use the hither-tither staff to get there quickly

(anyone else have any prep before the fight starts?)

Zenodor initiative 14

Pepin Init: 6

(Everything alright? It's been a bit quiet on the chat)

(ooc: Yes, sorry for long delays.)

Wyvern Riders initiative: 9 , 19 . and 10 

(there are 3 groups or clusters of enemies)

(also Randall and Tempe can now roll initiative too)

Randall Initiative:  5

Initiative 12

Round 1

Initiative Order:

1. Wyvern Riders (2nd cluster)
2. Tempe
3. Wyvern Riders (3rd)
4. Wyvern Riders (1st)
5. Pepin
6. Zenodor
7. Randall

(oddly the 3rd cluster is a ways off and won't be in position to threaten or join the fighting until the beginning of round 3... ???)

(Your turn DM)

(Just out of interest: Are we treating the Wyvern Riders as a single monster, or are we treating them as two separate things (a wyvern, and some character riding it). The reason I am asking is that I am wondering if we can do something like knocking the riders off)

There are 6 wyverns and 6 riders in each cluster, and they can be treated as separate creatures (dismounts possible).

Two each from the 2nd cluster target Tempe, Pepin, and Randall with Fire Bolt cantrips.

1st x Tempe: Attack: 13 Damage: 18 

2nd x Tempe: Attack: 19 Damage: 16 

1st x Pepin: Attack: 16 Damage: 15 

2nd x Pepin: Attack: 20 Damage: 9 

1st x Randall: Attack: 21 Damage: 18 

2nd x Randall: Attack: 9 Damage: 5 

(Tempe is up.)

Randall:

"Looks like they are hostile," says Randall wryly as the beams of fire scatter around him, none finding purchase.

Tempe dismounts, sending pinky the giant eagle to attack the closest wyvern  Beak. Melee Weapon Attack: Attack: 18 Damage: 4

Talons. Melee Weapon Attack: slashing damage.Attack: 24 Damage: 6

Flying alongside Tempe attacks the same creature 

Radiant Sun Bolt

Range

30ft.

Starting when you choose this tradition at 3rd level, you can hurl searing bolts of magical radiance.
You gain a new attack option that you can use with the Attack action. This special attack is a ranged spell attack with a range of 30 feet. You are proficient with it, and you add your Dexterity modifier to its attack and damage rolls. Its damage is radiant, and its damage die is a d4. This die changes as you gain monk levels, as shown in the Martial Arts column of the Monk table.
When you take the Attack action on your turn and use this special attack as part of it, you can spend 1 ki point to make the special attack twice as a bonus action.
When you gain the Extra Attack feature, this special attack can be used for any of the attacks you make as part of the Attack action.

The 3rd cluster flies closer but is still a ways off yet.

The 1st cluster pulls off veering left and launch two spells each at Tempe, Pepin, and Randall.

1st x Tempe is Fire Bolt with Attack: 9 Damage: Unable to parse dice roll. fire damage.

2nd x Tempe is Magic Missile with 5 force damage being dealt three times as a trio of magical darts sting you one after the other.

1st x Pepin is Fire Bolt with Attack: 22 Damage: 12 fire damage.

2nd x Pepin is Fireball with 22 fire damage to everyone within 20 feet of Pepin. DC 14 DEX save for half damage.

1st x Randall is Fire Bolt with Attack: 11 Damage: 6 fire damage.

2nd x Randall is Ice Storm with 9 bludgeoning damage and 12 cold damage to everyone within 20 feet of Randall. DC 14 DEX save for half damage.

(Pepin is up.)

Tempe looses concentration Pinky eagle, is now, Pinky, course thats not a bad thing 😉

Quote from Secretfool >>

Pepin creates his force ballista and puts it on his shoulder while he drinks the flying potion, thinking it will be usefull this time around. Although, for now, he stays on top of the main gate. Finally, as soon as the wyverns are within 300ft he casts Ice storm in the middle to target as many of them as possible. (20ft radius, 40ft high column)
DC21 dex save or take 30 damage (12 bludgeoning, 18 cold); half on success.

 Did this happen already? Or does Pepin still have the spell slot?

Dex save: 1

Zenodor targets the nearest group of Riders attempting to injure and ideally dismount them at the same time. He shoots a single beam of Eldritch energy at each of the three nearest riders

Beam 1: Attack: 18 Damage: 12

Beam 2: Attack: 33 Damage: 8

Beam 3: Attack: 28 Damage: 13

Any hit also pushes them directly away from Z by 10ft (no save), so presumably give the angle this means sideways and slightly upwards. So he is hoping that suddenly being 10ft away from their saddle (which at the same time continues flying forwards) will make them fall down. (And he rather maliciously hopes they do not have feather-fall prepared)

[Repelling Blast: When you hit a creature with eldritch blast, you can push the creature up to 10 feet away from you in a straight line.]

He then uses his Bonus action for a Telekinetic shove/push (whichever seems more likely given the nearest still-mounted rider) to pull or push one out if its saddle. 5ft, STR 18 save

[Telekinetic - Shove: As a bonus action, you can try to telekinetically shove one creature you can see within 30 ft. of you. The target must succeed on a STR save (DC 18) or be moved 5 ft. toward you or away from you. A creature can willingly fail this save.]