While we're sharing mythic+ fuck ups: those large elementals in Heart? they split into smaller ones, which grow into large elementals if left alone. The tank decided to pull both large elementals, both packs of smaller slimes and a chunk of dragon whelps. Then the aoe kills the elementals and the Arms warrior dies, our aoe falters and bam. Something stupid like 12 of the large elementals then proceed to pinball us.
We only missed killing one and at least the reformed ones don't spawn small one supon death. But still, such a waste of time.