Strefan, Maurer Progenitor [Best Vampire Commander for Blood Token Synergy] Strefan s your guy if you prefer cheating high-mana threats into play rather than paying full price
The obvious play pattern of swapping the textbox of, lets say a Crab, with Ulamog, the Ceaseless Hunger, but Id rather turn planeswalkers or artifacts into creatures and swap the planeswalkers ability with one of my creatures
The same is true of Ellie, Vengeful Hunter, as she certainly has the potential to be a compelling sacrifice engine
Fear of Impostors
but it certainly isn't a card you're going to play on the first turn
You can, and probably will run your mundane mana rocks, but artifact decks have access to a host of powerful cost reducers that work exceptionally well with broken combo strategies