Illithids!

Passing through another chamber, the acid smell before extremely powerful. They eventually entered a chamber that was a huge lake of acid, with a slim, slippery bridge crossing it.

I have to admit to a little railroading here. The guys came up with some interesting options to bypass the bridge, including mass fly. In the end, Kuppies attempted an arcane portal. Much to his surprise, the portal only traversed half the bridge. His target had been modified by the psychic powers of a mind flayer. Once they crossed to the mid point, a group of Illithids, floated up from under the bridge, surrounding them.

I let the encounter go for a couple rounds, but it was getting late and I needed to leave the heroes with a tough decision. As Ekeraath readied a massive blast of melee ass kicking, the lead Illithid called for a parlay.