Gimmicky planeswalkers are ones that have a twist to them, only having negative abilities, maybe being an uncommon walker, a nonlegendary one, one centered around only zeroes, one that transforms, one that has a plus that can get it to an ult directly by adding loyalty counters, etc
This is of Common rarity
Game Changers for Atraxa, Praetor's Voice Edgar Markov The Commander 2017 set was all about tribal decks, each focused on a single creature type: cats, wizards, dragons, and vampires
For a normal set, this might be overwhelming, but in Ravnica, where only five color pairs (and the five arcs of their intersections) are supported, this could be exactly what the doctor ordered
Tacking on the Root Sliver ability of not being able to counter the creature or any future creatures is certainly powerful as well