Draw:
Nissa, Vital Force,
Tireless Tracker (even more artifact synergies),
Horn of Greed,
Courser of Kruphix (kind of),
Omnath, Locus of the Roil.
Scroll Rack isn't card advantage, per se, but it does stack your deck Thrasios activations.
If you are running
Crucible of Worlds effects and don't mind a land tutor,
Elvish Reclaimer might be nice.
I also find your lack of some really, really good removal like
Decimate,
Reality Shift, or
Nature's Claim interesting.
Krark-Clan Shaman is kind of a board clear, yeah, but it's a 1 time thing (he kills himself) and you could lose a lot of rocks in the process.
Gemrazer is also super sus. I may just not be seeing it, but why are you playing a 3 CMC, sorcery speed
Naturalize? I don't really see any other Mutate payoffs, so is making Toggo into a 4/4 really worth paying extra mana and losing the ability to play your removal at instant speed?
Broken Bond, while also sorcery speed, at least gets you another rock and doesn't cost 3 mana, if you want a piece of synergistic removal.
In term of landfall triggers,
Tunneling Geopede could be cool, turning all your fetches into a
shock to each opponent's face, but I don't see anything else super crazy that is missing.
Reckless Fireweaver is nice for damage with rocks, but not a landfall trigger.