At just four mana, Halana and Alena can come down as early as turn three more often than not with some mana ramp, and then immediately start turning things into a threat
This makes prowess best used in decks with few creatures but multiple cheap spells that also replace themselves by drawing additional cards
This is so good it's been banned in formats
When [c]Yawgmoth, Thran Physician[/c] is paired with any creature with undying, such as [c]Young Wolf[/c], you can continue sacrificing the same undying creature over and over again
Like I said in the general overview, almost all land matters decks make tokens, and this just helps them rumble over the opposition, especially the sizable tokens Yuma makes
While it requires a bit more effort than its peers, Diabolic Servitude more than makes up for that in longer Commander games