The drow ambushes in the UD are way off the charts, spawning a stack of archers some of which get 39 AB, and they all hit 20-30. If immersion or danger is what it's aimed for, it only achieves in being unnecessarily dangerous, they've spawned to me as early as teen levels, and still do at 21.
It feels like when the rare encounters were first implemented, so I hope their spawn rate and power are adjusted properly.
