War of the Spark

Flux Channeler | Creature | Human Wizard | Whenever you cast a noncreature spell, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.) | Heonhwa Choe

Vizier of the Scorpion | Creature | Zombie Wizard | When Vizier of the Scorpion enters the battlefield, amass 1. (Put a +1/+1 counter on an Army you control. If you don't control one, create a 0/0 black Zombie Army creature token first.) Zombie tokens you control have deathtouch. | Zack Stella

Devouring Hellion | Creature | Hellion | As Devouring Hellion enters the battlefield, you may sacrifice any number of creatures and/or planeswalkers. If you do, it enters with twice that many +1/+1 counters on it. | Bayard Wu

Evolution Sage | Creature | Elf Druid | Landfall — Whenever a land enters the battlefield under your control, proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.) | Simon Dominic

Gleaming Overseer | Creature | Zombie Wizard | When Gleaming Overseer enters the battlefield, amass 1. (Put a +1/+1 counter on an Army you control. If you don't control one, create a 0/0 black Zombie Army creature token first.) Zombie tokens you control have hexproof and menace. | Volkan Baǵa

Mayhem Devil | Creature | Devil | Whenever a player sacrifices a permanent, Mayhem Devil deals 1 damage to any target. | Dmitry Burmak

Leyline Prowler | Creature | Nightmare Beast | Deathtouch, lifelink {T}: Add one mana of any color. | YW Tang

Rubblebelt Rioters | Creature | Human Berserker | Haste Whenever Rubblebelt Rioters attacks, it gets +X/+0 until end of turn, where X is the greatest power among creatures you control. | Tomasz Jedruszek