Been experimenting a lot with the Slimepede mission to try for Prismatic Slimes.
Farming Prismatic Slimes Tips
I found all 3 times they spawned on the same place. The raised part of the arena in a spot that usually doesn’t have a pot. Vyrne will also alert you to the Prismatic Slime’s spawn with an audio line.
You can see the Rainbow eyes/ face poking out before you strike the slime but otherwise i think it is in a standard pot.
All 3 times i got the same loot: 1 Ambrosia, 3 Damascus Ingot, 5 Azurite’s Splendour and 500 Knickknack Vouchers. Not sure if this is set loot or not but would like to hear your thoughts.