September 28 2020 changes:

Flamekin Harbinger -> Mana Crypt
Chord of Calling -> Sol Ring
Multani, Yavimaya's Avatar -> Triumph of the Hordes

The two tutors don't really do a lot and with the meta kind of knowing the power of the deck, it makes sense to try to win as fast as possible, thus the added ramp.

Multani, Yavimaya's Avatar never did anything really super useful and was just in there because I liked the card, but I was never really happy to draw it, Triumph wins you the game outright in the best case and in the worst case I can kill one or two opponents and mop up the rest in the next turn without breaking a sweat.

The number of lands is at the low end for an Omnath deck, but it generally feels like enough for my meta.

Testing as of October 21 2020:

Creeping Renaissance -> Ancient Greenwarden; also considering cutting Titania, Protector of Argoth instead of Creeping Renaissance.
Parallel Lives -> Scapeshift; Doubling tokens IS fun but Scapeshift just wins - especially with Valakut and Dryad out (long shot, I know)
Doubling Season -> Garruk's Uprising; I realized that drawing cards has become much more important with that list than doubling your tokens, I have not drawn DS or PL in months and have a decent win rate (also for some reason people target you when you resolve a Doubling Season)

Testing as of November 27 2020:

Hammer of Purphoros -> Kamahl's Will

Not sure what to cut for the Three Visits reprint... maybe Farhaven Elf (though it is a chump blocker)

Recent Updates as of October 01 2021:

Fertilid -> Three Visits (I love Fertilid but this makes the deck a bit more streamlined)
Naya Panorama -> Arid Mesa (Obvious improvement)
Myriad Landscape -> Prismatic Vista (... duh)
Ingot Chewer -> Foundation Breaker (1 colorless mana more is a small price to pay for the added flexibility)