Pairing it with Portal to Phyrexia allows you to repeatedly bring back a devastating control piece to crush your opponents' board states
Jerren, Corrupted Bishop / Ormendahl, the Corrupter There are better ways to manage the sacrifice creatures, lose life, gain cards, gain life, repeat structure of black decks, but Jerren, Corrupted Bishop is one of the more flexible versions of that
Mono Red and Izzet Prowess have benefitted from a slow accumulation of excellent low cost spells over several MTG sets: while Cori-steel Cutter is plain cracked, it's the sheer volume of high quality cards laser-focused on an aggro strategy that mean these decks are dominating standard
Both Dragons Rage Channeler and Ragavan, Nimble Pilferer are cheap and offer gameplay outside of kill your opponent as quickly as possible. As a result, weve seen a rise in midrange archetypes that have these three cards at their core, and Modern is better for it