Was pulling some rats on the left wall as you enter. No issues. Merc would pick them up and dps them down. An add came at me (one of these) and I expected the Merc would simply pick it up and tank it.
Nope! 45 second fear into the canal picking up every mob on the way.
No idea how I zoned back out alive, but I can tell you these things area nasty. Stay away unless you are hunting them specifically.