Thundemma Spoilers ahead for my party

So the party is 4 (sometimes 5) level 10 adventurers who are stacked with gear both official and homebrew. (To give a rough gauge, a single Androsphinx is well beyond a deadly encounter and two of them demolished it in 2 rounds while the others were frozen in fear doing nothing)

The context: They are in the Underdark and the fight will take place over a chasm filled with “mojoules” like Mojo from Crash of the Titans/Hextech from Arcane. These balls are solidified magic and one even the size of a golf ball can alter reality, and there’s some here the size of a car.

Hiiiighly magical stuff, extremely dangerous. This encounter should be one they genuinely consider running from. I have no idea what kind of creature goes here whether it be just pure magic beasts but idk how that would work or if it’s a defender if sorts guarding them? Idk I need the help pls and ty