This is my 1st Guide, on how to easily Pull SM cathedral fairly easy.
(I searched the forum with "Scarlet", "Monastery", "Cath", and came up with nothing.)
Requirements:
-A level 80 Death Knight
-A Frost Specc (You will need Hungering Cold and pref. Icebound Fortitude)
-A PvP Trinket (If those Frostbolts actually DO hit you, they can slow you down, and that isn't good.)
-Health Potions (This is really optional, I never used them, as I used the Death Pact + Ghoul Glyph trick)
To start off, when you go in to the Instance, you need to kill all of the mobs in the hallway. Use abilities that give you Runic Power, like DS, PS, Icy Touch...
When you kill them, (If you're boosting someone) tell your friend to stay near the Entrance, just to be safe.
Now, run to the Gate and don't aggro anything, because if you do, you can't open the Gate without wasting your Hungering Cold.
When you come to the Gate, open it and run to Mograine. Attack him with an Icy Touch and then kill him (Note that you will have the whole Cathedral attacking you, you shouldn't AoE Yet).
When the High Inquisitor opens her door, get her to low hp, and when she stuns you, (DON'T USE YOUR TRINKET, YET)
you'll notice that when she goes and ressurects Mograine, you're stunned and here, your HP can drop quite low. When the Stun duration is up, run to them, and use Hungering Cold.
This will trap everyone near, except the Bosses, so you should be able to run away.
Run out of the Cathedral, and here is where the magic happens;
Your aggro range is bigger and you begin to Aggro a lot of Mobs (The big group behind you will pick up everyone else), now you should have still more than 40 RP, and here is where the Ghoul Glyph comes in.
Summon your ghoul and use Death Pact immediately; INSTANT 40% hp! And there you go, now all you have to do is jump down the Fountain, go to the Hallway, and do a LoS effect, (Use Icebound Fortitude, if you need to) and wait for the mobs to come.
You will aggro all of the Mobs, so prepare to lay down a DaD, use some Blood Boils, and when they start to disperse Use Howling Blasts or just spam Blood Boil =P.
If there is something you don't understand, I'll post a video on Youtube, showing my DK doing this.
Additional Notes:
-The PvP Trinket can come in handy if you get stunned while running away from the Cathedral.
-Use Health Pots ONLY IF YOU NEED TO, you don't want to waste money on SM Cath, trust me=)
-This IS my 1st guide, so please don't be mean, I spent a lot of time typing this, so if it sucks, say so, don't go like "OMFGSUCKHAHANOOB GTFO FAIL!"
-I discovered this while boosting my friend, so IF it in fact is a repost, at least I didn't copy it =/.
-This COULD be done with other Classes, but I don't know, because I've only tried this on my DK... You are welcome to try it though ^^.
SHORT VERSIONFor those who don't like to read a Wall of Text.
Hallway: Kill them all, fill up your RP and prepare for Step 2.
Garden: Don't aggro anything, open the Gate, and prepare for Step 3.
Cathedral: Go to Mograine, Kill him, when the Inquisitor comes, make her stun you, and prepare for Step 4.
Cathedral 2: When the Stun stops, run to Inquisitor and use Hungering Cold.
Cathedral 3: Run Forest, run !
Fountain: Jump down the fountain and then Raise your Ghoul and use Death Pact.
Hallway: Stay behind a wall and when they come use DaD, BB, HB and all other AoE Effects.
Hope you liked it and uh... Yeah =D