Try out this:
1. Use Army, let Army tank the Boss until you get the plague.
2. Join that carnage and let the plague jump over.
3. Wait
4. Eventually the plague might hit you again, which is probably painful if it has already reached >10 stacks or so (I guess ~15 should be survivable at 90), so take a purification pot with you and use it. Its effect is simply dispelling yourself. Do NOT use the pot if you are sure you can still survive the damage, like when it hits you with only 6 stacks or so
5. ???
6. Profit
Wrynn looks easy, but just time eating. Also, nice chat overlay