Challenging solo content. The campaign is brain dead-easy.

If that's too much to ask for then maybe make the extremes or coil as a solo version with AI companions.
I love the design of those fights but without a "gaming is my life 24/7"-static group you have to deal with the randomness of other people dying to landslides and whatnot. The hardest difficulty spikes would be fun to play on even the most brutal settings cranked to max if I knew it's really up to me to win and not just pray for competent DF members.

Titan EX is actually a fun fight but DF makes it a wrist slitting exercise in lottery patience.