The above shot shows Wing 1 with the rest of the castle hidden. Using a key dropped off the Gatekeeper, the raid progresses into a basic "trash" room (purple, above) that has an opportunity to set the tone for this wing.
The two encounters of this wing are the Hall of Arms and the Library, and both of these encounters are gauntlet style events. Rather than having preliminary trash packs of their own, their 'rooms' are the events. Thus, beforehand, we have an opportunity to expose the raid to the types of mobs they will be encountering in these gauntlets, so that when the gauntlet begins they aren't caught off guard with brand new mob types.For that reason, I propose the following mobs be present in this 'warm up' area:
Hall of Arms / Armor Suits:
Heavily armored suits standing on pedestals along the walls. They come in various 'flavors', and each of these flavors are experienced again during the Hall of Arms gauntlet.
2h weapon (be it sword, mace, or axe) = Arms Warrior - has a Mortal Strike, and stacks bleed effects on those he hits. Thunderclaps to affect melee DPS.
1h weap + shield = Prot Warrior - Has a Shield Slam maneuver that removes (recastable, not flask) buffs, Concussion Blow that stuns the tank, and Sunders the tank continuously, reducing armor values. Spell Reflects occasionally to keep casters on their toes.
Dual wielding 1h = Fury Warrior - Flurries occasionally and has a Whirlwind attack that occurs after a short 'powering up' channeling animation. Uses a basic Cleave attack that causes damage in a frontal cone, and Intercepts lowest on threat from time to time. Enrages occasionally, which can be Purged, Traq Shotted, or just ridden out.
Also, any of them could Execute the tank if he tank falls below 20% if we're feeling especially hateful :)
As mentioned, the suits of armor line the walls at designated intervals. I imagine after a while, people will avoid pulling these, which is fine. They're basically there to get your feet wet, and understand what's coming in the Hall of Arms. There, you'll be fighting these same mobs with a twist (the floor activates, more on that later). Blizzard has moved away from rep grinds inside dungeons, which is fine, so there wouldn't really be a reason to clear this entire room. At the bottom of this page, I propose a possible solution to that in the form of a repeatable side quest.
I imagine the basic difficulty level to be about the same as Bog Giants in the Underbog were to a five man. Immune to CC, hits like a truck, can two shot unprepared tanks. The ones that intercept probably wouldn't end up smashing a clothies face in, but would just intercept over there and maybe toss a light cleave out to keep people on their toes.
Library / Undead Packs:
The Library area contains packs of undead minions that rush through mazes of bookshelves during its event, so here would be a good opportunity to introduce them, as well, in a more basic premise.
The mobs consist of a few variations (the links point to existing models already in the game):
Shrieker - Your basic 'ghostly apparition' that shoots spirit bolts and drops fear bombs. They never travel alone, and are susceptible to Shackle and Turn Undead. They can be handled first, or last, but are a huge hassle when loose, especially when one can fear the group into an Armor Set it's not prepared for.
Deathly General - These definitely should be handled first, because they will raise any nearby corpses to join back in the fray. This is a one second (kickable) AoE cast. If not kicked or Shield Bashed, you'll be back in the middle of everything you just killed.
Castle Keepers - Basic grunts. Can come in the humanoid spellcasting or undead melee variety, and basically 'fill out' the trashpacks.
Library Staff - silly little skeletons that run to and fro in the room from bookshelves that are placed along the walls. They can chain two pulls into one if the raid isn't careful. They're easily destroyed, but just love to run towards another group when alerted.
These library packs patrol around inside the room, or are statically placed in between the entrance and exit doors of this trash area. The armor suits line the walls.
As mentioned, the basic premise of this area is to get the raid comfortable with the mobs they'll be encountering shortly in the gauntlet events ahead. Raids will eventually work out how to skip certain pulls, but that's the nature of the game.
Sidequest - "Overdue Book"
An interesting idea would be to have books scattered around on the floor in this entire wing, and perhaps a bulletin board at the very entrance listing the title of a missing book. In a fashion similar to Karazhan, looting the wrong book would give you a curse or debuff, while finding the correct book (and turning it in to an NPC at the end of the Library) would grant access to a reward from the Lost and Found... one extra item, for going through the hassle of finding the book. Perhaps the book's mouseover tooltip indicates the title from afar, or maybe the raid needs to clear all the way to each book they see on the ground. Perhaps the raid doesn't even know what book they're looking for until they defeat the librarian and can check all the books they collected along the way against the 'missing books' post at the end of the wing.
Regardless, it's an option, and gives players a reason to not skip trash pulls earlier on.