Ok, this is the first post Im in here, I been learning Wpe and study though a lot of Skill Wbesite for 3 months. But now I really find this site is the best one, so I want to share something I think might be useful. Sorry for my bad English.

This works on Mangos, so far I know.
You need Emu, any version is Ok.

How to make the boss start at 35% health, here we go.
1. You have to kill this boss once in recent days. Let's say, Kel'Thuzad in NAXX. Go with a raid of numb, kill it. Go to the position where the Boss stand, record it in Emu, name it like A, then go away 30yard away from this point, and record it, name it like B.

2. Group some ppl who you can trust, must have a tank a healer and serveral Dps and everyone has to have EMU.

3. Go into the instance, in old days, the visiable distance in anyplace is 200 yards but now is just 80 yards, damn it. just stay far away from the boss you want to kill. Tank select point A and healer select point B.

4. Tank go first then healer go after 1 sec. Remember, tank has to see the BOSS die once before or it will NOT work.

5. Lol, the boss has just 35% left, enjoy killing it.

So far as I know, this works on Mango, I didn't try on other version. Dont spread this bug or it might be fix soon.