Andarious

Thanks, that's actually really helpful without being too much of a, "just build a different deck altogether".
I've made some according adjustments.

You could run some cards that make each player draw, with Psychic Corrosion that gives you an even faster way to end someone's deck.

Bone Splinters could work here.

I moved Touch of Moonglove to SB and put in Tragic Slip, the former is only good if I have a creature and by then it's kind of win more, not win. The later however provides some rather strong hard removal.

Whoever told you that is your enemy.

Thanks, tbh I was hoping for criticisms not compliments, is that weird? I am curious of any swaps or adjustments people might make for it.

Sadly the newer spell says "You gain 3 life" not "target player"

Oh, yeah for Eater of Days as well Fabricate's a good card.

Inventors' Fair as a 1 or 2 of. Also Academy Ruins

Maybe Fabricate but you're only running a small number of artifacts so probably just the lands.

Not really sure why you need 1 of Rites of Spring. If not it would be modern legal, then your modern deck could beat other modern decks (and cost $7). I do have to question how strong the decks you're beating are though.

Clever use of Torpor Orb, might just screw over your opponent as well as allowing you to get beefy creatures cheap. Consider any tutoring for it?

Hate doesn't matter if you just killed your opponent(s).

Triumph of the Hordes? Could do a handful of Overrun like effects.

That's a solid approach too.

Most folks who use Omnath use him as a sort of Voltron core/battery combo.

Things you'll probably want
Ramp (anything that adds more mana, particularly land)
Protection (things that prevent Omnath getting removed, hexproof, and indestructible are most common and usually pretty set)
Evasion (ways for omnath to avoid blockers or just go through, you'll use a lot of trample like Rancor, and Loxodon Warhammer for example)
Removal (Things that prevent your opponents from running you over, mostly with green you've got Artifact/Enchantment/Flyer removal, but you do also have Beast Within for single target anything)
Draw (You've got tons of mana so get creative, there are a few ways to draw based on creature power)
Recursion (Ways to get cards back from the graveyard especially key win con pieces).
Blockers (Just dudes that are good at getting in the way and hard to get rid of)
Any card that does more than one of the above, of course

Just build up a ton of mana and make Omnath as big as you can and win via commander damage, while preventing your foes from doing anything too out of hand.

Also, Dusk//Dawn is huge for you.

I love me some Doran.

Consider Hexproof equipment as well as or instead of Shroud. Also indestructible would be a nice layer of defense to drop on Doran but it's not that big a deal if you can't.

Urborg, Tomb of Yawgmoth would be nice to have with Pestilence

I love the low and mean curve. Can for sure come out of no-where and demolish a table full of players. Pretty vulnerable to creature removal, but a smart play will avoid that.

Academy ruins would be solid for you.

Consider Paradox engine for combo with Isochron Scepter which is painful to be on the receiving end of. You'll also probably want a few more mana-rocks, and since you only need blue mana you've got some good low cost ones out there.

Probably also worthwhile to add a handful (4ish) mass draw spells too, things that draw you 4+ cards or X cards, yes you have a good draw mechanic with your commander but he can still get removed if you run dry.

Could use some acceleration and board clearing, that's for sure.