First, there needs to be something worth copying when it enters the battlefield
By reducing your own spell costs while you tax opponents, it forces the game to slow down on your terms and makes it extremely difficult for other decks to resolve key spells efficiently
Adopting similar text as seen on Platinum Angel, Herald of Eternal Dawn boasts that you cannot lose the game where your opponents cannot also win the game, giving you a lifeline if you need another turn (or so) to win
Mephidross Vampire plays super well with Triskelion, though many casual playgroups frown on combos like this for being too easy to assemble
No, not the one youre thinking of
Drawing cards, stocking the graveyard with creatures to reanimate later with countless black spells, whats not to love