Sephiroth, the Savior (Atraxa, Grand Unifier) Atraxa, Grand Unifier decks tend to be flicker soup exploiting the obscenely powerful enters ability on their commander
New planeswalker commanders are always a pleasure to see, and leaves-the-graveyard matters is an interesting design space with a ton of potential applications that can take the deck in a variety of directions
You also get to cast that card without paying its mana cost when the Spelljacker attacks
Needless to say, despite this deck having alternative strategies, it still slows down massively without a constant Rotpriest on hand
Bam, five life right away but no chance on more life to come without some kind of Flicker effect
Preordain and Serum Visions are a nice balance of being able to afford lots options and information while also remaining self contained and easy to max the power potential