Because Copycat goes into every deck!

This is pure GB Counters (no delirium, minimal energy) with 2 copies of Saheeli Rai and Felidar Guardian jammed in for free surprise wins. Sounds disjointed? It's really not. Oath of Nissa means we don't care about Saheeli's colors and we can scrounge up 1 white for Felidar Guardian easily enough when the default deck already runs playsets of Aether Hub and Servant of the Conduit. The rest of the deck is optimized for generating massive advantage in counters and card draw through creature ETB triggers, which can be replicated by both Saheeli Rai and Felidar Guardian, making these cards excellent for the deck even when not comboing off. In fact, Walking Ballista is the only permanent in the deck that doesn't benefit from being copied or blinked itself (however, it is also the permanent that offers the most benefit when you blink your other permanents, being absolutely the best place to put your +1/+1 counters and always drawing you a card with Armorcraft Judge). Don't forget that the cat can also blink Nissa, Voice of Zendikar, allowing you to minus her twice in one turn. With even one Winding Constrictor out, that puts 4 counters on every creature.

Obvious upgrades: Fatal Push and more Verdurous Gearhulks, which are a bit over budget for me at this time.

Sideboard coming later.