3 groups of 65's - AA's not required but useful.
Easy: Most of West Wastes except Za'Yth and the new giant. Protector Kloie. Keo Kodal in Wyvernfang. East Dragonhorn mini's. Emerald maw, Freeport nameds. Slavemaster/Fluxator in Stormkeep, Lord Eldenal.
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You'll need your low tier raid gear and a tank with some early archtype aa's would help a lot.
Less Easy-Medium: Za'yth, Ancient Deepfiend, West Dragonhorn wing (Viz/Rhizal), Enforcer, High Priest Coralsha, WW giant, lower plane PoA nameds
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Tank needs all his defensive AA's starting on this tier. You;ll also need a decent chunk of your raid AA'd as well and have some good dps. If you can keep the tank healed you can probably outlast these encoutners but it may be close.
High-Meidum: Rymaz, Plaguefang, 3 frozen (Stormseye), most north Dragonhorn named, hunter of souls (HoMisery), original minor Towers of Agony encounters except dblash.
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This is the seasoned raid tier. All this stuff and some of the above mobs will be getting you geared up for the most extreme and ridiculous fights on the server. You need THE CORE of your raid geared as well as possible and with all their critical AA's and your casters with a good number of relic spells.
Hard: Dblash, Yziar, Advisor, Grand Librarian, 3 watchers (HoMisery), most upper plane PoA nameds. Gibberring Abomination, new Towers bosses except Warden. Master of the Everchill, Faralak
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These are just a bit tougher then the above ones. Considered the "end of tier nameds"
Harder but not extreme: Empress, Zirvane, Dergalak
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Basically once you get to this level anything can potentially drop your tank no matter how many hp or ac he has inbetween CH's and you need a fully geared and AA'd raid with all the right combonation of classes. Also the encounter themsleves are designed to wipe you until on each phase until you manage to survive and learn them all so you can do what you need to do to avoid the wipe ~_~.
.Extreme: Warden of Torment (ToA), Shadow of Misery, Guardian of the Sun Shrine (EC), Keeper of the Gates, Manifestations, Mirror Golems and everything else inside the Prison.
Impossible: Future encounters with gods.