For most early raiders, Anub'Rekhan will be the first boss they encounter as they step into Naxxramas. You can find him in the Arachnid Quarter. This is the 25 man (heroic) version of the boss. In the 10 man (normal) version, he does not start with the 2 ads on either side.
Anub'Rekhan has started and what you're seeing here is phase 2 of the encounter. He'll be chasing after the main tank. Meanwhile, he summons an extra helper that the raid is busy fending off. Watch out for Locust Swarms!
Heigan is the second to last boss in the Plague Quarter. He is a test of the raid's ability to coordinate themselves in communication and movement. Move swiftly and don't stop during the "dance" phase!
Be prepared before you drop in on him. He's going to come charging towards the raid the moment your raid is within proximity. Hunters, Frost Shocking Shamans, and Frost Mages will be putting their kiting skills to the test. Your tanks had best be communicating or else they may not live long enough to see the encounter through.
Maexxna is the last boss of the Arachnid Quarter. In the heroic version, she flings three players to the back wall whereas in the normal version she only throws one player.
Some players would argue this is the hardest encounter in the instance. Often cited as the "Frogger" boss, players will die the moment they come into contact with the oozes traveling from side to side. One player has already died from not being quick enough. Pay attention or else you may end up with some exasperated players beside you!
This is the first test your raid will face in the Construct Quarter. Patchwerk can make quick "werk" of your tanks if players aren't careful. Note the canals of ooze just in front of the group here. Melee players are advised to click off Fortitude and go for a dip before whacking on the boss.
Players can get themselves fairly close to the four horsemen without accidentally pulling them. Make sure players are in positions before engaging. These knights run to preselected areas in the four corners of the room.
Here we have two healers working one of the tanks for the Four Horsemen encounter. Watch out for any line of sight issues with the pillar and adjust yourselves accordingly. Avoid the void zones on the ground.
Instructor Razuvious makes his home training his students within Naxxramas in the Military Quarter. Death Knights will recognize this character from an earlier part of the game. This is the Normal (10 man version) of the encounter. Note the two crystals on the side as they will be important in controlling his students. In the Heroic (25 man version) of Razuvious, the crystals are removed and he has four students. Don't forget to bring two Priests!
Thaddius is the last boss within the Construct Quarter. The secret to this boss is to think back to the days of Heroic Mechanar where players had to stand in certain positions depending on what charge they had. Little does this raid group know, an imminent raid wipe is about to occur.
The room looks seemingly empty except for bones scattered everywhere. Make sure your raid is buffed and ready to go before stepping inside. For the unprepared, you might be in for a fairly nasty surprise.
One of the most famous encounters you'll find in Naxx is that of the Four Horsemen. It requires an unbelievable amount of coordination and communication among your raid in order to successfully kill them. Veteran Naxx raiders will notice that the style will be similar and not much has changed.
This is the home of Kel'Thuzad. His guards stand vigilant on all sides of the room ready to aid their master when called. Don't intentionally pull them just yet. They will come to you.
Sapphiron is slowly coming together. He is the last boss you will face before tackling Kel'Thuzad himself. It is a fairly random encounter. When you see a Blizzard coming towards you, don't forget to run!
Doesn't this remind you of the old days of Upper Blackrock Spire? These dragons probably stem from the same breed. The raid is here waiting for the go command to begin engaging these oversized drakes. We have to clear out all of them before pulling Sartharion or else they will all come running towards us.
Vesperon is a mini boss you'll run into as you clear the mobs within Obsidian Sanctum. Depending on the difficulty level, you can leave Vesperon and any number of the other two mini bosses alive. In doing so, you get access to additional pieces of loot.
This is the main boss of Obsidian Sanctum. He stands alone on the island for a strategic reason. When your raid gets to him, they will have to fight him here as well. Keep an eye on the sides for walls of lava as they run through the raid. Look for gaps in the fire wall and seek shelter in them to avoid being knocked back into the lava.
Here is the raid entrance to Malygos' lair. You can't summon Malygos directly unless you have the key from Sapphiron.
Poor Malygos. He has lost his sanity and guards what little of his domain he has left. He flies around a centralized platform where the raid will form up on.