In the majority of cases, entrance into these games requires some form of payment, be it in-game coins, the gem microtransaction currency, or a 'draft token' you can earn through the Mastery Pass
Outside red, every other colour is important
If a player creates a token that's a copy of Xantcha, the player who creates the token is its owner, not the player under whose control it enters the battlefield
You get to trigger its explosively recursive ability whenever it mutates, and you can use cards like Buried Alive or Final Parting to tutor creatures into your graveyard that later can enter the battlefield for free
Oh hey, the AI can do that too
If that Elemental still isn't a creature when the ability resolves, the ability won't deal any damage