In terms of common removal, both Caustic Exhale and Dragons Prey are solid options
A Display of My Dark Power A Premonition of Your Demise A Reckoning Approaches All Shall Smolder in My Wake All in Good Time Approach My Molten Realm Because I Have Willed It Behold My Grandeur Behold the Power of Destruction Bow to My Command Chaos Is My Plaything Choose Your Champion Choose Your Demise Dance, Pathetic Marionette Dark Wings Bring Your Downfall Delight in the Hunt Embrace My Diabolical Vision Every Dream a Nightmare Every Hope Shall Vanish Every Last Vestige Shall Rot Evil Comes to Fruition Fear My Authority Feed the Machine For Each of You, a Gift I Am Duskmourn I Am Never Alone I Am Untouchable I Bask in Your Silent Awe I Call for Slaughter I Call on the Ancient Magics I Delight in Your Convulsions I Know All, I See All I Will Savor Your Agony Ignite the Cloneforge
Beating 4C Omnath Before you can go about stopping the Omnath deck, you first need to understand its strengths
Reveal the top five cards of your library
For this reason, this card really only slots into white decks that have lots of low-cost creatures and plan to go wide
Also consider some of the more esoteric ramp options, like Lotus Cobra and Azusa, Lost but Seeking, that support a deck looking to play lots of lands