Upkeep Control (Legacy)

This is a control deck which uses various effects to produce large amounts of mana early in order to hard cast the various win conditions. The idea is to lock down your opponent and then kill them using interesting mechanics that exploit the absence of the Upkeep phase.

For example:
Breeding Pit + Contamination neutralizes almost all non-black decks.
Breeding Pit + Pestilence means you can deal as much damage as your mana-base -or life total- permits, and still keep pestilence in play.
Eon Hub can really change the game. It has obvious synergy with Contamination, Abhorrent Overlord, Kuro, Pitlord and Breeding Pit. It can also be used to stop Phyrexian Arena from killing you and of course stop your opponent's upkeep effects.
Gray Merchant of Asphodel + Breeding Pit + Recurring Nightmare means you can make your opponents lose life and gain life yourself each round.
*Rite of Belzenlok is an alternative to Breeding Pit, it doesn't last forever but it is better if you intend to drop Eon Hub to cement your strategy and just need a few turns to build up to it.

Then there are some support cards like Phyrexian Arena and Beseech the Queen to keep your hand full and find what you need, Consume Spirit to gain life and maybe deal considerable damage, No Mercy to protect you from creatures you can't block and Perilous Vault for that necessary board wipe.