Omnaths color pie is highly versatile, which opens up lots of doors for deckbuilding, but I prefer to focus on ramp and control in this case
For this reason, decks of three or more colors are quite popular

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If we play them, we gain life and draw cards, both worthwhile things
In the case of Charge Across the Araba, you can see what they were going for: attack with the team, bounce all your lands to buff everyone, win the game