Zimone, Infinite Analyst

$0.38

The first spell with {X} in its cost you cast each turn costs {1} less for each +1/+1 counter on Zimone, and casting that spell puts two more counters on her. The discount only covers generic mana, but that's where X goes, so a Zimone with six counters takes six off a big X spell. It works on any turn, so instant-speed X spells can grow her on opponents' turns too. The deck is full of hydras, X-cost card draw and ramp, and wants an X spell every turn.

In the recorded games Stonecoil Serpent and Walking Ballista were popular cheap triggers, since casting them for a low X still adds two counters to Zimone. Lightning Greaves kept her alive while the counters stacked up. Games followed the same curve: slow early, then a midgame turn where Zimone was big enough to cast a huge hydra or draw spell for next to nothing. Removal on Zimone reset the whole engine, so protecting her mattered. The deck won through large creatures and card advantage rather than a fast combo.