It's Frost Damage achievement bug (Heroic Deadmines)

[lordryan555]

In heroic Deadmines while fighting Admiral Ripsnarl I jumped to the position shown below about 3 quarters through the fight and received an achievement that would otherwise be impossible to get with the gear available in the game right now.

[grimmeged]

why not just line of sight the biggest of the adds.
you need 3 to explode then you can reset and kill the boss.

Too much effort for a real easy achiv

[Nitric]

Hardly an impossible achievement - actually one of the easier ones. You just LoS them when they Coalesce and it does no damage to you.