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Wildborn preserver comes out early and they put +1/+1 counters on themselves. Merfolk skydiver and Pollenbright druid put +1/+1 counters on themselves or anything else and Combine Guildmage ensures coverage. Evolution sage and Guildpact informant proliferate those counters with merfolk skydiver potentially allowing multiple proliferates per turn later in the game. Spectral Sailor is a 1/1 flyer (not bad just for that) but flash allows you to pump Wildborn preserver safely during opponent's endstep and (albeit garbage, but a potential bonus) card draw to get Oko out earlier.
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NOTE: Set by owner when deck was made.
growth spiral would help your sage proliferate more and also get more land out to get oko out faster.
removed 4x Benthic Biomancer- draw and discard wasn't used often
replaced with trollbred guardian. this way you don't have to care about deathtouch or leaving yourself vulnerable after an attack and having to wonder how many blockers they'll use
I made some edits, hopefully give you some ideas. I really like your deck!https://www.mtgvault.com/iskavan/decks/proliferate-2020-pgb5534/
Evolving Wilds would be nice for the evolution sage