Patchwerk Tactics

"Behold, Patchwerk. When word of his existence first reached the ears of the Brotherhood, none believed the tales of an abomination with such immense speed and strength. Fewer still believed it when he fell the first time..." - Commander Eligor Dawnbringer

Patchwerk is, put simply, the gear check of Naxxramas. He has no crazy abilities, no special adds, no dances or other unique gimmicks for his fight. He hits hard. He hits fast. That's his special ability.

ABILITIES
Hateful Strike - Patchwerk will use this ability every 1 second, hitting the person with highest health in melee range for 27,750 to 32,250 (25 Player: 79,000 to 81,000) physical damage, mitigated by armor. As a physical attack, Hateful Strike can be dodged, parried, or blocked. This ability also adds threat to the top 2 (25 Player: 3) people in Patchwerk's threat table.
This ability is what makes Patchwerk dangerous. The first thing to notice is that it goes off every second. This means that Patchwerk will be dealing extreme amounts of damage very fast to the Offtank, while the Main tank will be taking less so damage. Your stronger geared tank should actually be the Offtank in this fight, even if it means pulling blows, the offtank will be taking more damage.
The next thing to note is: This ability also adds threat to the top 2 (25 Player: 3) people in Patchwerk's threat table. Once Patchwerk gets a few hits in, The tanks will be threat locked by this ability. DPS should have no fear about pulling threat after the first few seconds, and should be burning any cooldowns or abilities they have to kill Patchwerk faster.
The Third thing to note about this ability, is that it is a physical attack. Tanks who stack avoidance will more than likely have a higher chance of survival, as Hateful Strike will be avoided more, causing less stacking damage within those 1 second periods, and giving your healers more time to react to the damage.

Frenzy - When Patchwerk is down to 5% health, he will Frenzy, a soft enrage, increasing its attack speed by 40% and damage done by 25% (Hateful Strike included).
This is Patchwerk's frenzy ability, and it'll make him hit very hard. He uses it at 5%, so the best way to survive it is to blow any healing or defensive cooldowns here, and Pray that your DPS can kill him before he slaughters the tank and then the raid.

Berserk - 6 minutes after engaging Patchwerk, he will Enrage, increasing attack speed by 150% and damage done by 500%, wiping the raid almost instantly.
Slime Bolt - After Patchwerk Enrages, he will start casting AoE Slime Bolts, dealing 8,325 to 9,675 Nature damage, and applying a damage-over-time effect for another 5,700 to 6,300 every 3 seconds, to the whole raid.
Essentially, this means that 6 minutes after the fight, there will be no chance of survival, and Patchwerk will murder your entire raid in almost seconds. This enrage timer cannot be fought, you have to beat it or you WILL be killed.

STRATEGY
Patchwerk is not too hard if your gear is able to handle him. He relies totally on the numbers output of your raid and their ability to competantly do their role.

DPS should understand that a few seconds into the fight, and the tanks will be entirely threat locked to the Boss. You can afford to wait 5 seconds and then attacking, as it will ensure that the Tanks have aggro and patchwerk doesn't go rogue and murder someone. DPS should wait a few seconds, THEN blow all their abilities and go crazy.

This cannot be stressed enough, a few seconds after the fight starts and Patchwerk is threat locked to the tanks, you need to be using all your DPS abilities to beat the enrage timer, and this is a perfect mechanic to ensure you can do anything you want without fear of pulling threat.

Tanks, you should take care not to step into the green goo when pulling Patchwerk. If you do, Patchwerk will likely one-shot you while you're at half health.

Beyond that, Tanks should understand that the Offtank will be taking more damage, and the better geared tank should try to stay as the second in threat.

Use your defensive cooldowns effectively, keeping in mind the 5% frenzy when you do use them, and understand how hard and fast Patchwerk will be hitting you. Survival should be your first priority since Patchwerk will keep your threat up for the most part.

Healers need to be prepared to heal the tanks as hard and fast as possible. Through this whole fight, only the tanks should be taking any damage, so use your healing effectively and keep the tanks from dying.

as Patchwerk reaches the 5% frenzy, all care should be thrown out the window in favor of spam healing to keep your tanks alive. Survival is key, DPS will not take ANY damage throughout the fight if you are doing it correctly.

Good luck.