The card is a bit clunkily worded, but in essence, it basically splits each player's creatures into two sides of the battlefield (or the "river")
Its a hilarious mash-up of sports memorabilia and Magic history, which makes this one of the quirkiest Secret Lairs ever
The ability that triggers on exerting it will resolve before blockers are declared
Death Clouds a nasty card thats only used by two types of players: those who wish to watch the world burn, and Tergrid, God of Fright players, who also incidentally love to watch the world burn
Starting at your Wilds of Eldraine Prerelease, you can distribute the following promos: Hornet Queen (printed in French) Harvester of Souls Kalonian Hydra (low print quantity, printed in Spanish) Goblin Rabblemaster For ideas on how to distribute your 30th Anniversary promos, you can always visit the Promo Usage & Policy hub
So, with that realization came the introduction of ability words --italicized words that group similar abilities thematically without carrying independent rules meaning