Sometimes what looks like failure at moving can actually be related to dispel failure. If someone gets a 10x stack of Snowflake on them, they cannot move. We said, "you'll get automatically dispelled if you also have the bubble debuff on you" (the snow patch doesn't appear in the bubble when dispelled), but there were a few times even that didn't go very smoothly.
Blackhorn
really isn't about DPS though. Sure, you need people that do moderate DPS, and not having melee is rather helpful. Well... except for Rogues. I almost always top the chart on Blackhorn (heroic or not), because of using Blade Flurry. My only qualm with it is that I'm never too sure if I should turn it off quickly when a mob charges and turn it back on after and if I should switch targets and possibly waste combo points? I might just need to use my points early and switch early.
But anyway... you also need people to soak the small circles, but then again... these same people cannot take the big circle unless they have a good cooldown (getting hit by the small circle gives you a +shadow damage taken debuff). Thankfully, as long as a tank is in the big circle (with an add), I can just pop Feint for a 50% reduction.
It isn't a
terrible thing if you miss a circle or two, but it will spawn fire on the deck of the ship. The worst part about the fire is that it's been bugged for quite awhile. Little gnomes fly around and put it out, but the fire doesn't visibly disappear even though it will not deal any damage to you. So, you may run through some fire and think, "hey, this isn't so bad", and then try it again and take ~50k damage per tick.
But back to the circles! You also need two people to go into one circle at a time, because they deal over 200k shadow damage. I could probably survive one on my own with a cooldown (since Feint only has a 10s CD), but that's probably not that common. So, you'll have to get your people to coordinate and pretty much create a buddy system.
To give you an idea, there have been plenty of wipes where the boat blew up on us. So, unlike normal, it will definitely take some significant damage if you're not careful.