The key to this achievement is that your group must already have the harpoons on them before the fight is initiated. Knowing that it can be reset by the group pulling back into the room that Gortok Palehoof is found in lets you keep your harpoons without dying or having to leave the instance and lose them.
After 3 assigned members of the group have 2 harpoons each (only 5 are needed to kill Grauf), he is reset and the group can quickly run past to the harpoon guns before he respawns. The tank positions themself in the doorway just next to the harpoon guns, and someone is sent to run back down the corridor and stand in front of Skadi to start the event, then quickly make their way back up to the group at the harpoon guns.
As the fight is started, the group should allow Skadi to do one pass by (watching for frost breath) so that the adds can be DPS'd down. As he reaches his second pass, the harpooners should shoot Skadi down and the tank should pick him up. Then all DPS goes to the remaining adds and kills them to stop them causing trouble, then Skadi is killed as normal.
A regular DPS group with no special tricks should be sufficient to kill Skadi in well under the time limit, even when he is allowed to do one pass by.
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