Milling your opponents deck is an easy and surefire way to make sure they dont have the ability to come up with a response to your damage
Santa is magic, and also omniscient, which means hes basically God, so bringing people back to the dead fits the character perfectly
Ephemerate doesnt save your creature from a board wipe, but Eerie Interlude does
They frequently have abilities like unblockable, flying, or deathtouch, allowing them to slip past defenses and apply consistent pressure
Blue can be oppressive to fight through for Red, Boros, or Gruul decks
First it immediately replaces itself drawing a card, gaining 4 puts you out of reach of Lava Spike (Omnath, Locus of Creation + Fetch Land is usually concession from Burn decks)