Boss abilities: Basic melee and Hateful Strike -- that's it. Hateful Strike is a wow powerleveling nasty melee attack that Patchwerk attempts to use every second, targeting the highest-health player in melee range who is not the tank and within the top three (or, in Naxx-10, top two) of Patchwerk's threat list. Hateful Strike also increases the amount of threat held by the top three (or two) players on the threat list, so you don't want your melee to start DPSing Patchwerk before Hateful Strike is firmly on both offtanks.

Tanks: A main tank and at least one offtank are required, preferably two on heroic. Tank damage on the MT is high but steady. The offtank is there to absorb Hateful Strikes. Tanks' emergency buttons like Shield Wall, Barkskin, Icebound Fortitude, etc. should be saved for the last 5%, as Patchwerk gains an undispellable buff called Frenzy, and his damage and attack speed both increase substantially.

DPS: Your job is simple; unload. Try to time your cooldowns and trinkets to have them up as much as possible. If you have a Shaman, Heroism/Bloodlust timing is key. If your raid is still gearing up and not likely to kill wow powerleveling him with much time to spare before Patchwerk's 6-minute enrage, use it as soon as the tanks have adequate threat, and then use it again as soon as it comes off cooldown. Hunters and moonkin will want Scorpid Sting and Insect Swarm respectively up at all times.

Healers: You should have at most three targets to heal on this. All damage done by Patchwerk is melee, so ask your mages to cast Amplify Magic on the tanks. More than anything else, the offtanks wow powerleveling absolutely must be kept topped off as much as possible, or Hateful Strike will start to find targets among the melee DPS. Pre-healing is key. Hateful Strike can be parried and dodged, and it's not unusual to see tanks have both good and bad avoidance streaks. Don't let a good avoidance streak lull you into a false selse of security. In Naxx-25, a bad avoidance streak on the first offtank will usually lead to the second offtank soaking more Hatefuls, so be prepared to see that.