Hello. I thought I would compile all the changes I know to the heroic raid encounters in Cataclysm so far. Lots of threads asking for information and few of them that actually offer any input in these regards. Here I go:
Magmaw - Adds spawn regularly that leave behind a trail of fire that hits for 50k+ every 0.5 sec. These adds need to be DPSed and the encounter is a DPS race in that regard. The last add has to die when the new ones appear. At 30% heavy spreading required as Nefarian does aoe splash damage to random people
Omnitron - Nefarian teleports everyone in the middle of the poison clouds when they appear. The thing that healers and dps needs to stand in acts as a defile and people must be ready to move on a moment's notice. Static charge target gets an extra debuff which does aoe shadow dmg to everyone - the further away from the debuffed target any player is the more dmg the aoe does to him.
Also, players targeted by acquiring target can not move, instead the whole raid has to move
Maloriak - extra DARK vial, that spawns high HP adds that need to be brought down before the next vial gets thrown into the cauldron. They leave shadowy defile-looking things behind them
Atramedes - Fiery imps spawning randomly from the fire that explode for unhealable aoe damage when they reach their targets (unslowable?) The round objects, Sonar Pulses that come from underneath Atramedes no longer disappear so fast, but are left bouncing from walls to walls. Players have to DPS Atramedes while ignoring at some point 20 Sonar Pulses? It seems they disappear after roughly 1 minute while new ones keep coming.
Chimaeron - Continues to attack the tanks during Feud and during the 25% phase everyone loses HP (2k every 2 seconds?) so it is a huge DPS race
Nefarian - lots of new mechanics, other than that ??
Halfus - there is no longer a given setup of drakes, but you can free all of them. Freeing the drakes also has more effect than when you free them in normal mode.
Valiona and Theralion - You now have to go into the Twilight realm and kill all the mobs there. A new debuff that leaves a huge void zone behind when it explodes, dealing moderate damage when one person (the one with the debuff) is in it, but fatal damage when more than 1 person is in the void zone. Breath is now 270 degrees, instead of 180
Ascendant Council - Lots of new added mechanics. Gravity Core and Static overload have to ball up on each other as soon as possible, else one of them deals heavy damage to the whole raid. Time to move together - 3 seconds from the moment the last person got the debuff? Phase 2 is no longer 1) get wind 2) get grounded 2) get wind 4) get grouded, but depends on the emotes, sometimes you need to get grounded 3 times in a row. A new emote means that you have to renew your buff, so when you just got grounded and the emote says get grounded again, the last grounded debuff disappears and you have to get it again.
Cho'gall - A totally different encounter from normal mode?
Conclave of Wind - no information
Al'Akir - DPS requirements foresee the encounter being done in such a way that the Feedback buff cannot disappear from AA. Also 2 Squall Lines together in p1 and p2.
All of these are of course in addition to the HP and damage increases. Feel free to correct me in some points or add to these changes.