Drive Me Crazy (10 player)

This is a farily simple achviement if you have the keepers to help you during the fight (namly Freya)

In Yogg-Saron's room you will see green pillars of light, when you stand in them you regain sanity(being a debuff during the entire fight), on normal this is about 10-20 Sanity a second.
So aslong you got Freya and people keep an eye on their debuff this is one of the easiest Achivements in ulduar.

If you kill Yogg, you're probably going to have this. One insane member really makes the fight hard, both from lack of dps/heals/tank and from the extra damage he's unloading onto the raid and easily wipe it.

As far as I know, no-one knows for sure because Yogg-Saron has yet to be tested on the PTR. (Edit: And isn't going to be.) My search-fu fails me, but as I recall, MMO Champion datamined some of his boss abilities a while ago, and when a player goes insane, they fall under the control of Yogg-Saron until the end of the fight (or until they die, presumably.) That may well be wrong - correct me if it is.