Interesting. The deck has a lot of playables and I could see it going a few ways.
The two cuts I would spot immediately are
Crush Dissent and
Firemind Vessel. Vessel is the worst of your four(!) mana accelerants, Dissent doesn't really fit your deck since you hardly play on the opponent's turn (
No Escape is alright though).
I do think your deck has more than enough permanents for
Bond of Flourishing to be a card I'd always want to run (also gives your Narset another target, which you should be concerned about).
19 creatures is definitely to many, especially seeing how you have cards like
Narset, Parter of Veils and
Flux Channeler in your deck. You want a high creature count due to
Band Together,
Jiang Yanggu and
New Horizons, but we should trim down to at least 15 creatures. For now, I'll trim one of each of
Primordial Wurm,
Wardscale Crocodile,
Iron Bully and
Snarespinner.
This would put us at the following 25 cards:
1 x
Sky Theater Strix2 x
Kronch Wrangler1 x
Pollenbright Druid1 x
Snarespinner1 x
Flux Channeler2 x
Arlinn's Wolf1 x
Iron Bully2 x
Bloom Hulk1 x
Centaur Nurturer2 x
Wardscale Crocodile1 x
Primordial Wurm1 x
Narset, Parter of Veils1 x
Jiang Yanggu, Wildcrafter1 x
Dovin, Hand of Control1 x
Jace, Wielder of Mysteries1 x
Arlinn, Voice of the Pack1 x
Bond of Flourishing1 x
New Horizons2 x
Band Together1 x
No EscapeThis seems like a decent baseline, and there's a few different ways to go from here. I'll line out my way of thinking from here.
Seeing how you're fairly low on interaction and how it can enable and sometimes even trigger Proliferate, I think I want to add
Teferi's Time Twist to the deck. It's a card I generally don't like much, but I feel like it could work really well in your deck (For instance, time twisting a Bloom Hulk puts two +1/+1 counters on it by itself).
Another interesting thought would be adding
Arboreal Grazer over the other Snarespinner. Again, not a card I generally like much, but we need some early drops to put Yanggu or New Horizons counters on, and this one can sometimes accelerate you into these. It does need +1/+1 counters and some Proliferate triggers to be an efficient card, but then again, Snarespinner is not much better off.
My last three cuts after that would probably be the other
Primordial Wurm (you can maybe cut that card from the 42 in general), maybe the other
Iron Bully (it fits your deck very nicely, but it probably is your lowest power level card) and maybe
Dovin, Hand of Control (I can see it being useful to blank an opposing attacker and even attack ito it, but it seems like the least impactful card in your deck).
So, the final product in my case would look like this:
1 x
Arboreal Grazer1 x
Sky Theater Strix2 x
Kronch Wrangler1 x
Pollenbright Druid1 x
Teferi's Time Twist1 x
Bond of Flourishing1 x
Flux Channeler2 x
Arlinn's Wolf1 x
No Escape1 x
Narset, Parter of Veils2 x
Band Together1 x
Jiang Yanggu, Wildcrafter1 x
New Horizons2 x
Bloom Hulk1 x
Centaur Nurturer1 x
Jace, Wielder of Mysteries2 x
Wardscale Crocodile1 x
Arlinn, Voice of the Pack8 x
Island9 x
ForestI decided against running Interplanar Beacon. With all the early game Green cards we really wanted a ninth Forest, and the Island helps cast more cards than the Beacon (Beacon helps cast Jace and Narset, Island helps cast these plus all of the other blue cards), something a couple points of life don't compensate for.
The main alterative to this build is to cut Narset and run a more creature heavy build (something like Dovin/Primordial Wurm > Narset, Iron Bully > Time Twist, Snarespinner > Grazer, maybe another creature over No Escape). I don't think I like that build as much, but YMMV and I can't deny it's there.
Definitely an interesting build, and IMO not one where there is a 100% clear best deck.