Those 2 achieves are indeed bugged, but they are not broken.
Skadi -
Start the fight.
Gather 5-6 harpoons then give them to 1 player.
Die. You cannot just run out of the dungeon to reset the fight or the harpoons disappear. If you die then run back in, you keep the harpoons.
Go back in and have the tank grab all aggro of all mobs, and spam the turrets as fast as you can, the second Skadi is within range. Click all 3.
If done fast enough, he will give achievement when killed.
Novos -
You need decently geared dps for this, and you don't need a tank.
Position 1-2 dps at the entrance to the room to catch the 4 Guardian mobs the second they spawn. You can't let them enter the room.
Position 2-3 dps on the stairs. None of those mobs can touch the ground below stairs.
Healer needs to be in the middle of the 2 dps groups to be able to heal.
As soon as the 4th Guardian dies, the boss' shield drops and the boss fight starts.
Boss needs to die within 8 seconds of his shield dropping. You cannot let him summon any adds.
(his summoned adds count as mobs touching the floor")