Fiery Confluence: I almost put this card into its own section, since it isnt necessarily a sideboard-only card, but it certainly fits the role of utility card exceptionally well
The precon deck came with a few landfall creatures in Avenger of Zendikar, Scute Swarm, and Rampaging Baloths, so it was an easy call to throw in a few more
Eminence is an incredibly strong ability, as you dont even need to cast this vampire progenitor to make a zillion tokens in Vampire decks
Again, the Warp ability really helps it here since you can set something up early and the angel can come back later
Protective Embrace, which allows you to apply Ward to other characters you control
The way this card handles countering spells in red is precisely how you would expect it to- by allowing the controller of the countered spell to cast a random spell instead