Hammered Breakdown

~~~Step 1: Use the ladder to the right of the main fort entrance to avoid triggering the dialogue with Alexander and the soon-to-be-exploded Lizard

~~~Step 2: Make a mostly-melee party. My team was:
Me - Summoner (Important for Totem Spam, but you could easily sub in a Ranger instead)
Ifan - Polymorph (Important for CC like Atrophy and Chicken)
Fane - Fighter (Important for Knockdowns and Fortify)
Sebille - Assassin (Good burst damage)

~~~Step 3: Get the Teleport gloves from the crocodiles

~~~Step 4: Get to level 5 by doing everything before you leave the fort.
IMPORTANT: If you leave the fort by any means (i.e. you make any kind of escape) then Dallis leaves! Make sure to save and check the entrance often if you're unsure!

~~~Step 5: Use crates and barrels on the island to seal yourself up on the parapet where you fight the card cheats (and where you came in at Step 1)
It's important to put the blocking items at every entrance, including the ladders. You can test if it's done right by trying to move past them. If so, you won't be able to reach it. This makes it so the enemies bunch up outside the fort wall and thus are out of the combat until you choose to teleport them in.

~~~Step 6: Arrange your three other party members to be in the little tent lean-to thing on the parapet with a gap to the back of the tent.

~~~Step 7: Teleport Alexander into that gap between your party members

~~~Step 8: Get away from the ledge!

~~~Step 9: Wail on Alexander and use CC the moment you can. DO NOT OVERLAP CC TO AVOID RUNNING OUT!

~~~Step 10: Dallis eventually teleports him away and does something Spoiler-y

~~~Step 11: Achievement!

~~~Step 12: Teleport up enemies one by one and burst them down (especially the hammer's pets)