I can confirm that Vessel is easily duoable by two enchanters. Feyenu and I went down there this morning with two charmed guards and owned him. Fight took under a minute. I tried to land 5 slows during the fight, but all were resisted. So he's probably unslowable like others have claimed.
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He could probably be soloed if you didn't have a charm break during the fight. I felt kind of bad for the tracker down there that was asleep at his computer, though. For anyone else caring to track him, he was killed around 8:30 AM EST this morning.