For the stuns, how about increasing the cooldown for every stun ability while in Rambo Mode for non-Rambos.
Double CD timer for starters?
Only thing I can think of at present is where everyone who gets teleported into the area will get a fairy like effect.
It could be possible to tie it to the quest so when the Event finishes or "Time Over", the effect is automatically removed.
Alternative, everyone could get different skills, but it should be like "Rambo Arena" only.