This Omnath gets brought down simply because its so narrow compared to its contemporaries
Of course, you don't care about that downside if you're playing cards from your graveyard, and that's exactly the kind of playstyle this card enables
Note that there are tons and tons of creatures with mana sink abilities that let you pump the creature up, whether that be Walking Ballista, Chameleon Colossus, or dopey creatures like Carnivorous Moss-Beast
Good Mythical Morning Table of Contents show What Is the Mystery Booster Set
It's main use is to be super fun with things like Well of Lost Dreams ("Instead of drawing this card, I'll gain life and also draw cards!") Sadly, you don't have blue in your color identity, so you can't play Drogskol Reaver, but for redundant copies of that effect, you do get Dawn of Hope once Guilds of Ravnica releases and even Lich's Mastery if you're crazy enough