Prince in Karazhan is one such boss. No matter what method you pick of fighting him, the post, the door, moving, the back wall, whatever... there's a component of luck. We've all had that happen, where the infernals just seem to follow your pack of DPS... or your tank.
You can be doing everything EXACTLY right and still wipe multiple times due to sheer random gimmick!
I have encountered another gimmicky boss! The first time for me, though I've done Violet Hold maybe three times?
That's right. I'm talking about Zuramat the Obliterator.
(There he is, right above. Look at the evil glowyness of him. JUST LOOK IN HORROR! (and how I wish Bargrave looked like that!))
For those not in the know, he's a void walker boss that's found in the Violet Hold instance within Dalaran.
He summons little void sentries, who are invisible unless you are the lucky person he gives the void shifted debuff to.
These sentries do a shadowbolt volley every few seconds unless the person who is void shifted kills them.
The boss also does Shroud of Darkness, which can stack on a player up to 5 times, for 20/40/60/80/100% reduction in healing recieved, if you hit him while he has this activated.
We had a poor group for this. We had THREE melee (tank, two DK), one caster (warlock) and one healer (my shaman).
The first time around, he kept void shifting ME. (As the healer, I'm a little busy trying to keep people alive.)
After that, he shifted the warlock a whole bunch of times, the other DK a whole bunch of times, the tank once and never Seraphelia (Boonybaby).
We wiped ... 4 or 5 times on that boss.
The super-frustrating thing? These little void sentries have 500 hit points. Yeah, even I could kill one if I wasn't otherwise occupied trying to not let the tank or the DPS die.
I wasn't the DPS, and I wasn't watching what everyone was doing (busy healing, kthx!) but I would imagine that as long as they were vulnerable to AOE damage, Rain of Fire, Unholy Blight, Shockwave, Thunderclap, Death and Decay... all of that should work to knock out a bunch of them if you're one of the types of 'dps' (I include the tank in that) targetted.
But it's a gimmick. It's as much luck of who gets debuffed as it is skill.
A hunter gets debuffed, easy! Volley, Multi-Shot, hell, even auto-shotting would kill them, they just need to auto-shot, tab, auto-shot, tab, auto-shot, tab...
Finally, the tank calls it and I say, "Let's try to reset the instance, maybe we'll get a different boss?"
And the other DK says, "Yeah, it will."
And I look at him and say, "Why did you not tell us this important pertinent and worthy piece of information before now?"
"I thought you wanted to kill this boss." ... which while true, I DO want to kill this boss just so I can jump up and down on his corpse and crow with delight and glee, take screenshots and kick and spit on it a few times... but I'd also be just as happy to never ever have to fight him ever ever again.
Hate gimmicky bosses!