Swashbuckler or Kill Dallis Lady Vengeance No Deathfog - Divinity Original Sin 2 Definitive Edition

What you need:
1. Teleportation
2. More than 1 character
3. Cloak and Dagger
4. Haste and Adrenaline (Optional but very helpful)

How to step by step:
1. Teleport the enemy near the ballista
2. Go to the lower deck
3. Sneak and go to the ballista
4. Use the ballista
5. Repeat with other characters

You can save before killing the last enemy and kill the last enemy to get Swashbuckler achievement and then reload to kill Dallis for max XP and 2 Unique items.
Total XP gain from Dallis: 30.300 XP + 2 Unique Items
Total XP gain from Swashbuckler: 27425 XP

The duration of this video before cutting and editing is 16 minutes so you need around 16 minutes to do this.

Timestamp:
0:00 Prebuff
1:27 Weird Weaponized Monk Turn
1:59 Cheese Start
4:37 Juicy Loots
6:24 Killing Dallis
7:07 XP Gain (Dallis)
7:20 Bonus Unique Loot (Dallis)
8:03 Swashbuckler Achievement
8:27 XP Gain (Swashbuckler)