Build a deck around instants and sorceries, and Delver of Secrets basically becomes a 3/2 flyer the turn after it comes into play
With five ninjas on the board, the player you just hit loses half their life
Of the existing card in Magic, our best options are spells that flicker creatures specifically back to their owner like Long Road Home, Turn to Mist, or Otherworldly Journey
The first being the aforementioned 20/20 Marit Lage token from Dark Depths
Split cards have historically had the issue of being too over-costed to offset the benefits of choice, and they almost always failed to be excellent early plays by design
1 generic, 2 Phyrexian white, Sacrifice two other artifacts and/or creatures: Put an indestructible counter on Mondrak, Glory Dominus