Level 12 Encounter (XP 3,500)
1 berbalang (level 10 solo skirmisher)
1 gibbering mouther (level 10 controller)
1 skeletal tomb guardian (level 10 brute)
I DM'd this exact encounter for my new group at 11th level. It was in a crypt, the berbalang was buying dead bodies that were supposed to be buried so he could eat their memories. Then he wrote books about them.
Anyway, the encounter was very fun. I like the duplicates, it really challenged the players, especially with the gibberling messing up the terrain.
He almost escaped too, but a choice saved encounter power of a spear in the back finished him just before he fled up the stairs and out into the night.
Only downside was calculating the hit points of the dupes, especially after he lost some hit points. That, and his lack of ranged attack (if I remember right).