I'm taking over the GM spot in a "Living Arcanis" campaign this coming weekend. The ground rules for this kind of campaign are that I not add or subtract critters or conditions from encounters in the downloaded adventures. That's fine with all of us.
The party: a 16th-Level psionic. His 14th-Level cleric cohort. A 14th-Level wizard. A 12th-Level fighter specializing in mounted combat. A 13th-Level gunslinger. A 15th-Level ranger with his 13th-Level druid cohort. A 12th-level fatespinner.
These guys plough through combats like a husky runs through snow. When they've been buffed for fighting, combats rarely get through the first round.
The adventure has them encountering a marilith demon (MM 44) in a big cave.
I'm trying to come up with strategies and tactics for the demon. Right now, the best I can come up with is polymorphing into something like a vampire, to draw the wrong kinds of attacks from the party.