War of the Spark

Bioessence Hydra | Creature | Hydra Mutant | Trample Bioessence Hydra enters the battlefield with a +1/+1 counter on it for each loyalty counter on planeswalkers you control. Whenever one or more loyalty counters are put on planeswalkers you control, put that many +1/+1 counters on Bioessence Hydra. | Mathias Kollros

Merfolk Skydiver | Creature | Merfolk Mutant | Flying When Merfolk Skydiver enters the battlefield, put a +1/+1 counter on target creature you control. {3}{G}{U}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.) | Sara Winters

Neoform | Sorcery | | As an additional cost to cast this spell, sacrifice a creature. Search your library for a creature card with mana value equal to 1 plus the sacrificed creature's mana value, put that card onto the battlefield with an additional +1/+1 counter on it, then shuffle. | Bram Sels

Roalesk, Apex Hybrid | Legendary Creature | Human Mutant | Flying, trample When Roalesk, Apex Hybrid enters the battlefield, put two +1/+1 counters on another target creature you control. When Roalesk dies, proliferate, then proliferate again. (Choose any number of permanents and/or players, then give each another counter of each kind already there. Then do it again.) | Svetlin Velinov

Tamiyo, Collector of Tales | Legendary Planeswalker | Tamiyo | Spells and abilities your opponents control can't cause you to discard cards or sacrifice permanents. +1: Choose a nonland card name, then reveal the top four cards of your library. Put all cards with the chosen name from among them into your hand and the rest into your graveyard. −3: Return target card from your graveyard to your hand. | Chase Stone

Kiora, Behemoth Beckoner | Legendary Planeswalker | Kiora | Whenever a creature with power 4 or greater enters the battlefield under your control, draw a card. −1: Untap target permanent. | Jaime Jones

Niv-Mizzet Reborn | Legendary Creature | Dragon Avatar | Flying When Niv-Mizzet Reborn enters the battlefield, reveal the top ten cards of your library. For each color pair, choose a card that's exactly those colors from among them. Put the chosen cards into your hand and the rest on the bottom of your library in a random order. | Raymond Swanland