[Modern] Fear of Missing JUND

Couple bits of potential synergy problems I see in the build as is. Delirium is gunna be very hard to get, as Zenith shuffles itself back into the deck, so you're really only running 4 sorceries (for this purpose), which means you'll be struggling for that 4th type. You're have critters and lands covered, but only have 13 other playable cards (15 if you discard a Zenith (other than Fear itself as an enchantment hybrid)) to use to get 2 more types in the grave. This is mitigated a bit by Zenith being able to fetch Grist and the few discard effects you've got, but overall seems unreliable to me. Delirium is usually cheated into by running Urza's Saga and sackable artifacts, which gets you 3 types for 1 card, but that would require lots of retooling for the deck. What would really be nice is if Break Out milled instead of the way it's structured, but then it would be worth 50 bucks and probably banned, so it is what it is. Alternatively, you could run Malevolent Rumble, and trade off the mill/token for the deeper reach and tempo, but that's a matter of priorities I suppose.

Second potential problem I see is the curve, which is pretty 2-drop heavy and very limited on acceleration. You can Zenith into Arbor turn 1 of course, but other than that, this deck will be playing behind most games without a turn 1 play, and most of your turn 1 plays are reactionary against critters. This is usually solved by running some mana dorks like Ignoble Hierarch that up your chances of a turn 1 accelerated play that's going to let you hit the ground ahead on turn 2, or 1-drop discard outlets like Thoughtseize or Inquisition of Kozilek, both of which deny opponent the turn 1/2 play they want to make to get their deck going. Obviously you're ok with a turn 1 Ragavan or fetch into surveil land, but the format's pretty god damn fast from what I'm seeing, and I don't think the curve as is will work out overall against decks that can go nuclear turn 3.

I'd personally cut 2 Dreadknights (1 copy is an engine by itself, and you'd rather Zenith into it than take the time early to play it as a sorcery) , a Fiend Artisan (useless early on, perfect Zenith target for mid/late game), and Unholy Heat (conditionally great, but less good as single spot removal in a format that can get around spot removal) for 4 copies of Thoughtseize, but that's me. That brings the 'I wanna drop this turn 1 for advantage' count to 10 cards (4 Thoughtseize, 4 Ragavan, 2 Zenith), which (in theory) will help the speed a lot.

Just the stuff that leapt out at me, not trying to throw shade at the build or anything.