The first two bosses you face will be chosen at random from a selection of four echoes of famous faction leaders. Each of them occupies one of four dragonshrines and comes with their own unique trash and abilities. They share a loot pool and in addition have a couple of unique drops each.
Echo of Sylvanas
The mistress of undeath shows up in the Ruby Dragonshrine. Her trash is pretty straightforward -- just large chunks of undead dudes that should be relatively simple to pull and AoE down.
Sylvanas herself isn't too hard to fight, and most of her gimmicks are a matter of staying out of the dark, undead fire. She does put out an couple high-damage shots you'll want to watch for. Use your cooldowns to help mitigate that damage. Also, watch out for the purple stuff when it spawns on the ground and stay out of it.
Her biggest move is going to be when she summons a ring of ghouls that slowly walk inward toward her. When they reach her, they explode. You can't just run out of the ring, though, because you will take massive damage. Instead, you'll need to kill one of the ghouls and run out through the small gap it makes in the ring. As a tank, it will probably be your responsibility to choose a ghoul to take down, so be sure to mark it and/or warn the others ahead of time to focus on your ghoul target.
Echo of Jaina
Jaina shows up in the Azure Dragonshrine. Her trash looks very similar to Wrath's Halls of Reflection trash, with ghostly footmen, priests, hunters, and sorceresses. Tanks, be ready to wrangle in the hunters and sorceresses, especially, and don't let the footmen get at your healers and casters, because they will bash and silence them. DPS, watch out for the lightwells the priests summon, and get them killed ASAP.
Jaina herself isn't too hard of a fight. Unfortunately, her Pyroblast and Frostbolt Volley cannot be interrupted. Pyroblast puts up a pretty nasty DoT on its target, so you may want to keep your defensive cooldowns ready for that. Of course, Pyroblast comes pretty frequently, so you'll spend large amounts of time with that DoT ticking away on you.
Her biggest move is a set of three Frost Blades that radiate out from her front and freeze anyone they touch. She'll always cast these after a Blink, so you won't be stuck in melee range when they come. Just find out where's blinked to and be ready to dodge the spikes. They move slow enough it shouldn't be a huge problem. In addition, she will also spawn bombs. If they are not prematurely exploded (by running over them), they will explode for massive damage to the entire group. Optimally, your ranged DPS will take care of these, but if your PUG mage is being extra slow that run, it's worth it even for a melee DPS to step back and run over and grab it. Your healer will thank you.
Echo of Baine
The tauren Chieftain Baine shows up in the Obsidian Dragonshrine. His trash is possibly the most annoying in the dungeon, with a Break Armor ability that devastates your defenses and the ability to summon fire pools that can wipe out your group pretty quickly.
The good new is that you can skip the trash if you're good. If you wait for the patrols to pass, there is a small window of time that you can run straight up the middle to the first island in the lava surrounding Baine. Of course, in a PUG, that's asking a lot, and there's always a chance someone will aggro something anyway, so you may want to clear it out after all.
Baine himself isn't a horribly hard fight for a tank. Your main quest is to keep him out of the lava, as it will buff him with a massive fire damage buff. Keep yourself out of the lava as well, as lava will give you a stacking debuff that causes you to take increasing damage from said lava. That said, there is one upside to standing in the lava: It will give you the same fire damage buff as it gives Baine. Therefore, physical DPS (such as death knights) should periodically step in the lava to renew that buff, and tanks (such as death knights) should tank Baine near the edge of the lava so the melee DPS can easily buff themselves.
Baine will occasionally jump to a player and sink the island they're on. He will, of course, automatically get that fire damage buff when that happens, so make sure he gets back to dry land and possibly have a defensive cooldown ready to weather the extra fire damage if needed.
Baine's specific loot has two pieces that are pretty good for us. Axe of the Tauren Chieftains is something you'll want to pick up if you never made it into Firelands. The hit and expertise may be just what you need to hit your soft caps. Bloodhoof Legguards provide a nice alternative for tanking if you haven't purchased your tier 12 legs yet.
Echo of Tyrande
Tyrande shows up in the Emerald Dragonshrine. Her challenge actually starts with the trash. The whole shrine will be dark, with the mobs rushing at you in total darkness. Tyrande will spawn patches of moonlight, though, so your basic strategy here is to gather the mobs and drag them into the moonlight so you can see stuff to fight it. It's best to stay bunched together as a group and, if you're the tank, be ready to grab random aggro off your healer especially.
When you fight Tyrande herself, there's not much you can do besides tank or DPS besides interrupting Stardust. Stardust should definitely be interrupted. She will cast it more than once every 10 seconds, though, so if possible, set up an interrupt rotation with other interrupt-capable group members.
As mentioned, the echoes do share a loot pool, and there are a few drops that death knights will like. Dragonshrine Sceptre offers a great option for dual-wielding frost knights; just reforge away the critical strike rating. Breastplate of Sorrow offers a DPS chest option, with critical strike and haste rating meaning it's nicely statted for the new unholy death knight. The Gauntlets of Temporal Indifference offers a nice tank set option. Finally, the Girdle of Lost Heroes offers a nice tanking belt upgrade for pre-Firelands tanks. You can also get the Time Strand Gauntlets from the quest Archival Purposes, which will serve you well if you never managed to get your tier 12 DPS gauntlets or need some extra expertise.
Storming the Bronze Dragonshrine
You'll fight the final boss, Muruzond, at the Bronze Dragonshrine. The big issue with the trash is that the first pull will have two caster mobs. You'll probably want to use a Death Grip/Strangulate one-two punch to get them wrangled up so you can burn them down. If you leave them be to target your DPS and healers at range, they will hurt.
With Muruzond himself, stay away from the bombs he spawns. Not only do they explode for mucho damage, but they create a patch of fire on the ground. DPS will want to stay away from the head and tail of the dragon, as both will do damage to you. Tanks will want to keep the head and tail pointed away from the DPS and healers.
Muruzond's big gimmick, however, is the hourglass. Every time someone hits the hourglass, the fight will rewind to a few seconds from the beginning, with one big difference: Muruzond will not heal. That means any cooldowns will be reset, any dead people will be resurrected, and all patches of fire on the ground will disappear. You should use your DPS and tanking cooldowns early and often, because they are coming back. Even Army of the Dead's cooldown will reset, though not every group will take kindly to your playing spin the dragon, so think twice before you use it.
Generally, you should assign the healer or one of the ranged DPS to hit the hourglass. They can hit it up to five times. You can use the hourglass hits as soon as everyone's spent all their cooldowns and the buffs have faded, or you can save the hits for when there are a few dead group members or too many fire patches to handle -- it's your choice. Regardless, this should be a pretty easy fight to conquer. As soon as the dragon's down, you'll be free to move on to Well of Eternity.
Muruzond's loot includes a few pieces of interest to death knights. Temporal Pauldrons and Crown of Epochs are great grabs for any DPS death knight who's been having horrible tier token luck. Breastplate of Tarnished Bronze and Chrono Boots are your tank drops.
Learn the ropes of endgame play with WoW Insider's DK 101 guide. Make yourself invaluable to your raid group with Mind Freeze and other interrupts, gear up with pre-heroic DPS gear or pre-heroic tank gear, and plot your path to tier 11/valor point DPS gear.