Patchwerk is a very simple yet very challenging fight (or at least he was back in the day). He hit the tanks very hard so he was a check on both the healers and the tank and there was a tight enrage timer which made for a tough dps check. If everything goes well, the tanks are the only people who ever take any damage in the fight.
There is only one mechanic in the fight and it is called Hateful Strike. It is a melee attack that does a ton of damage and it targets the person in melee range with the most health and the boss uses it roughly every 1.6 seconds. You need to have at least two tanks for the fight, one boss and one Hateful Strike tank. The healers basically just spam max rank heals non-stop on the tanks, no real complexity to it.
The most important thing in the fight is for the Hateful Strike tank (or tanks) to be topped off ASAP after getting hit. With Hateful Strikes coming as often as they do, if the Hateful tank doesn’t get topped off immediately, it is very possible for someone else in melee range to have more HP and therefore be a target for the Hateful Strike. If someone that isn’t a tank gets hit with a Hateful, it’s a one-shot.
One thing you can do to protect melee is to have them step into the green slime. The slime will reduce their HP by 50% and since there is no raid wide damage, the healers can ignore them. If the melee are getting heals from Improved Leader of the Pack or Vampiric Embrace, they can jump back into the slime occasionally to keep their health low.
While using the slime like that is a nice little trick, if it is really necessary, then you have other problems that you need to deal with – i.e. your Hateful Strike tank is not being topped off fast enough.
It’s basically a tank and spank fight. Assuming you have the gear for it, once your healers get into a rhythm, it should be free loot.