I upgrade 'Boss challenge' idea.
This challenge have 25-50-100(Idk) floors, each floor have different boss/bosses like denal/Katt/new boss/old boss, they have their special fighting style.
for example.
WORN BOSS - each time when its hp drop 10% it go underground and heal himself a bit and spawn on another location.
SLUG BOSSES(2-4-6 slugs) - when they all die they will combine and transform into a big slug,
DRAGON BOSS - when his hp reach 40% he start flying and his def and dodge increase.
CAGE BOSS(-,-) - Sometime it capture a player(for some limited time) and all dmg players do on boss, will be distribute(by %) between captured player and boss.
And we can go in party or solo(In solo, boss have less dmg and hp)[just suggesting solo challenge] After clearing a floor every pt member get gp,cc,exp and gold (Specially exp & gold)
I have some more crazy ideas for this 'boss challenge' tower.
{Sry for my bad English, If u don't understand then don't try to understand.