So I just tried sleeper again tonight and (assuming he doesnt path under the world) he's an extremely tough fight. I'm wondering if there is some strategy im missing (probably).
basically, I got him to around 45% but then ran outta mana. Second pull was just a nightmare. But the guy has a ton of HP. I'm not sure if he's just waaaay harder than the others, but I steamrolled all 4 warders pretty handily on my first trip ever to ST last night.
FWIW, im playing 12 characters, good balance and Im pretty much decked out in good gear for my level minus epic 2.0s (none).
The only strategy at all ive found useful is hiding the healers under the bridge.