This deck has a few different sub-themes to it, but generally centers around life gain/life loss mechanics and slowly wearing your opponents down until they die, while keeping their stuff in check. I play with it a lot within a casual setting and it's very strong, and in multiplayer as well, although people do seem to get annoyed and target me when things like Blind Obedience and High Priest of Penance hit the field.
It is standard-legal, although given the presence of some better/cheaper removal spells (i.e. Doom Blade, Go for the Throat, Mortify, etc.) in older sets, I often swap out some of the instants when playing in a casual environment.
Any suggestions or comments for this deck would be much appreciated, so feel free to leave feedback.
As mentioned above, there are several different things going on in this deck, and depending on the draws, it can play differently each game. In general, the action won't really start with this deck until turn 3, when you can start playing Nighthawks and Kingpins, but a turn 2 Blind Obedience will keep the other guy's creatures under control until you have something to deal with them. Although it's a two-drop, Vizkopa Guildmage is generally better in the late game, so I generally keep it in my hand for a while unless you really need a body on the field. Also, it's generally good to keep Bloodline Keeper in your hand until you already have three or four vampires out, because he'll be targeted pretty quickly. Just avoid dying early on and you should be fine as you acquire more board presence.
The sub-themes and combos are as follows:
Extort: An earlier version of this deck had a lot more extort creatures, but I ended up swapping them out in favor of stronger all-around creatures, (i.e. Vampire Nighthawk) so only a few cards use the mechanic. Nevertheless, it shouldn't be too difficult to keep a Blind Obedience, Kingpin, or Crypt Ghast on the field most of the time, and since a lot of mana will be going toward removal spells and more creatures, you probably won't need more than one or maybe two extort triggers at a time. Crypt Ghast is great for this; if you can keep it alive, it'll make the extorting even easier. Even though the deck isn't quite centered around it, it'll still wear down your opponent and pad your life total pretty consistently.
Vampires: Bloodline Keeper is a great card on its own, but with a couple of Nighthawks and Sorin on the battlefield, that 5-vampire quota to transform it should be extremely easy to reach most of the time. If you manage to get Lord of Lineage face-up, a small army of 3/3 and 4/4 vampire tokens with flying and lifelink distributed between them will be pretty frightening.
Spirit Tokens: In addition to the vampire tokens, it's always nice to have as many flying creatures as possible, and small flyers are particularly useful for chump-blocking. Lingering Souls is really great just for the fact that you can use it twice, and the cheaper black flashback cost makes it really worth it. Plus, both times it's cast you can activate an extort trigger. That'll give you a pretty decent supply of tokens, and if Requiem Angel gets onto the field, the death of any of your other creatures will just make more of them.
Infinite Combo: Vizkopa Guildmage's second ability and Exquisite Blood are great on their own, just to keep your life total safely ahead, but once you have enough mana you can trigger both of them with just about anything (extort, Tribute to Hunger, Obzedat, combat damage) and that's the game.