I'd swap at least one, possibly two, become immense over apostle's blessing.
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I don't think phytoburst will ever do much. I'd drop them altogether in favor of rancor. The trample damage will help push your poison through. Secondly, you probably have a tad too much pump/protection. I would shave some number of vines, mutagenic growth, and prey's vengeance (maybe 4/3/0 of each) for spell pierces. Hope it helps.
I really like the transformative nature of this deck. It plays totally different when boarding in the Nahiri package which I imagine comes as a shock for your opponents! As for the construction, I read you have a few cards specific for your meta, but I really wouldn't want crumble or palm maindecked. I'd probably just run a couple "value" Nahiri main with the aforementioned cards in the board. Another thought I had was gitaxian probe for free tokens and it adds a small boost to consistency. That's all I got. Certainly looks fun to play.
Electrolyze would be a better fit than lightning strike. Additionally, might as well run delver.
4 sulfuric vortex is too many. It really becomes dead in multiples plus you really only want 2 lands the entire game. I see PoP in the SB but it is a star in legacy. I'd certainly maindeck them.
I really like the addition of DRS. I may test that out myself. I would up the count to 4 however, since you are running rooftop storm. I would certainly add cabal therapy too, even as a SB option, because some games more control elements are necessary.
Lake of the dead would be pretty sweet to power out your finishers.
I love seedguide ash for flavor. This deck certainly cannot go without "high tide" in the SB.
I think you have plenty of bolts/removal. Thalia could bump a couple FoD. I can't see a scenario where you'd want to draw more than one of those per game.
I would def play Thalia since this is such a creature-heavy deck. I don't see the need for path to exile. You have bolts to clear a path for your attackers. If your opponent gets a creature in play you can't handle, by then you should have overrun their board. Maybe a SB option if playing Goryo's vengeance for an early Griselbrand game 2/3.
I made a deck similar to this once. I would swap wrench mind in favor of stupors. I also prefer cabal coffers in this deck over Nykthos. Lastly, they aren't as potent anymore, but sinkholes might be an option too. Just food for thought!
I feel like duress could be dropped since you run hymn, thoughtseize, and the therapy. Maybe some blue card draw, perhaps intuition, would be a nice addition. Thinking outside the box, sinkholes would be nasty in the SB. Btw I love legacy and I wish I could afford this deck!