Random Generator gave me Armageddon Clock and Volrath's Vanguard card. Originally, it added one counter during your upkeep, but changing the trigger added a little more Volrath, and opened it up to be very explosive. I may have undercosted this, considering that it could turn into a "return your graveyard to your hand every turn" sort of effect, but it would probably need to be tested to prove that.

­Volrath on the other hand is an interesting Vanguard card... but it took me all of 20 seconds to figure out how to break it, and I'm quite sure there are better ways than mine as well. Add Future Sight (or Magus of the Future) and any 1cc creature that sacrifices for a decent effect. Death Cultist seems fine.

I like the card, though I think it should be more intensive. I would like if it cost life for the last ability, though the Clock only costs mana. Wording-wise, I think it would be better as:

"Whenever a creature you control dies, put a doom counter on Volrath's Slaveyard.

At the beginning of your upkeep, for each doom counter on Volrath's Slaveyard, you may return target creature card from your graveyard to your hand.

­: Remove a doom counter from Volrath's Slaveyard. Any player may activate this ability."

yeah making the last ability cost 1 or 2 life rather than 4 would make it feel much nastier.
heck, since its a slaveyard maybe "sacrifice a creature: remove a counter... etc" would even work. But I agree with Dude, should be "whenever a creature you control dies" otherwise it is bonkers in a sac deck (or maybe just non-token creature as I can see this going nuts with Eldrazi spawn)

Oh, yes, "dies". I forgot that word exists. "You may" makes sense as well. And, yeah, we can make this more black while we're at it. Added.

I looked it up. Evidently, whenever a creature goes to the graveyard, now, it dies. It isn't different than sacrifice effects, so that really doesn't change anything. For example, they didn't change the functionality of Archon of Justice when they reprinted it in 2012 with the new terminology. It still works when you sacrifice it.

As for the loss of life part... I don't know. To me, paying is nastier. If my opponent sacrificed 4 creatures, and all I had to do is pay 8 life to stop him from getting more creatures every turn, it wouldn't be a problem. If I had to pay a total of mana, though, it would be a big problem. To me, forcing a person to commit a lot of mana has a better chance of making this get out of control, and forcing interesting options. With the loss of life, the question becomes "Would I survive if I lost this life? Because I'd rather lose 19 life than let my opponent start to return his creatures..." not much of a decision, really.

That being said, Black already has a punisher theme running through it, so I might do it anyway, just to stay on theme...