Just wanted to point out having 20/20 poisons means nothing and is proof of nothing, you can buy more than 20 of each type of poison... I carry 40 wound on my rogue most times since I use it 99% of the time. He easily could have poisoned his weapons and then topped up on poisons, or been carrying 21 of each.
Also, the counter attack thing he uses to avoid pvp flag while attacking guards would be
Riposte, it's a pretty well known trick amongst the pvp community.
The swimming thing most likely has to do with having the deserter buff or all his equipment being red (IMO not worth it since under water breathing really isnt that big of a deal, specially for undead).
Mounting inside objects, just the same old geometry glitch that's been in wow since the dawn of time... this will not work in a lot of places, it really is fluke and depends largely on how big your character model is and how big your mount is. Lots of other videos make use of the very same bug by getting in and behind geometry.... think of the world you see in wow as cardboard layers, if you can find some way to squeeze behind or above a layer, it's easy to slide on the other side and then you are free to move as you want.
The afk in BG thing, he's got the deserter buff, which to my knowledge is not the same as the debuff you get from being flagged inactive in a BG, I'm thinking that one is VERY likely a private server as there should be no way you can enter a BG with the deserter buff on. The debuff you get from being flagged in a BG means you get 0 honor but it's not deserter to my knowledge.
I have no idea how he's doing the direct flight thing, but I have heard of that before and to my knowledge it's a very old bug.