Sigmascape V1.0
Unlock
To unlock Sigmascape v1.0, the questline for Deltascape V4.0 (A Void at All Costs) must completed.
Questgiver: Cid @ The Yawn (closest Aetheryte is The Peering Stones in The Fringes)
Next quest: "The Anomaly" which sends you back to Rhalgr's Reach to talk to Jessie.
Next quest: "Return to the Rift" from Jessie. Completion of this quest will open up Sigmascape v1.0.
Strategy
Shoot the train and don’t stand in the AOEs. There’s a stack marker that’s a column rather than the usual roundy bit. Sometimes spotlights will chase you for a bit and then leave a puddle (like the fire in the Ala Mhigo scorpion fight), try to place the puddle on any ghosts in the arena to disperse them.
If you touch a floaty ghost, you and the ghost will get teleported into a sleeper car (to get out, kill the ghost and exit via the aetherial clicky), so try not to.
There are a few adds to clean up, and then you get to jump up on top of the train and kill a Doom Chimney! Yay!
After the Doom Chimney, you hop back down and everyone gets a debuff that kills you if it stacks too high (like the suffocating toad bubbles in Rabanastre); face plant into a floaty ghost to be teleported into a sleeper car and clear the debuff.
Then you go back to shooting the train and avoiding AOEs and dispersing ghosties with puddles of light.