Let's take a look at some more GU Frog cards you might want to use with Grolnok, the Omnivore.
Of course, there's the recent Croaking Counterpart from Innistrad: Midnight Hunt. Make frogs with superpowers, only there 1/1 creatures.
Omnibian can turn another creature into a 3/3 frog until end of turn. Species Gorger can return a creature to your hand at the beginning of your upkeep.
Of course, you can always go Sultai and use Grolnok, the Omnivore and The Gitrog Monster in the same deck. They're both from Innistrad, after all.