Baron Rivendare A-Z
This is NOT a guide to help you get your mount by bugging out and skipping through doors or just exploiting through. Do not think that.
What this is is simply the quickest way to legitimately farm the Rivendares Skele-horse.
Note: This is aimed for hunters, but is applicable for anyone who can dodge around mobs and/or get out of combat easily. This is applicable to most anyone who can AoE decent amounts of mobs. if you aren't a hunter simply replace the hunter spells with your class AoE spells and disregard all other hunter things as they aren't necessary for a quick Baron run.
First: Getting the key. Simply go in the front way, dodging around mobs until you get to the church. Since you didn't go through the side entrance the mob is still there. Kill him and loot the key.
Now with the key you can simply go in the side entrance after the initial run. The side entrance is to the northeast of plaguewood.
Second: Now dodge around the groups and use your new key to open the first gate. Move through and unlock the next. Now, run left from the gate to the first boss. Once at him Feign Death to disperse the following mobs. The boss should only take maybe 10 hits to down easily. Go inside and kill the acolytes by rounding them up and AoE'ing them down.
Third: Go back up dodging groups and run left again over to the banshee. Again, feign death, then kill the boss. Do not use a pet or the banshee will Mind Control you and then reset the fight. Down her and kill the acolytes once again.
Fourth: Keep going until you get to the boss. Feign death then round up the boss and the mobs on the steps and AoE them down. After the mobs die focus fire the boss. Try to interrupt his Frost Tomb spell if you can, because it freezes you taking away precious time. Kill the acolytes and the slaughterhouse is ready to be slaughtered.
Fifth: With the slaughterhouse door open keep going and enter. Send your pet to attack as many abominations as you can handle and AoE them down. Keep doing this until they are all dead. Then an abomination boss will come out of the slaughterhouse. Kill him quickly. Next a wave of undead will come to attack you.
Set down an Explosive Trap and cast volley once and they'll go down immediately. Finally after several seconds a group of 5 skeletons will come out of the slaughterhouse. These have very low health but can hit decently on a level 80, but not enough to worry about. AoE them down.
Sixth: Finally the door stands open. Go in and sit on a bone pile to the right of the door. Get mana/hp then send in your pet.
Nuke him down, and when he summons a group of skeletons AoE them with a volley before he can death pact them.
If you can do this within 45 minutes you also get + 300 Argent Dawn rep, which is useful for several achievements. All in all I can do this run in about 10-15 minutes.
With this and a drop rate of around 1% then it will take you approximately 1000-1500 minutes, or 16.8-25 hours as one of the worst case scenarios. Generally I see people get this mount within 10-20 runs as of the new patch.
Good luck on getting that horse!