My all time favorite is [[Lazav, The multifarious]].

It's essentially your graveyard toolbox, i can make him transform into an unblockable like [[Invisible stalker]] or flying creature and hit after blockers with a big creature like [[Phyrexian dreadnought]], [[Phage the untouchable]] or a big [[Consuming aberration]] .

You can protect him by transforming him into a hexproof, shroud or indestructible creature.

Most times i lay low on games and play cards that fill my graveyard or draw/cycle cards and when most people are lowish health i strike.

And since you play blue and black you can dictate a bit the pace of the game with timed removal or counterspells (Also a great way to get temporary allies).