Grunn, the Lonely King [Dominaria Prerelease Promos] Judge Gift Cards 2004 You and that opponent each

You and that opponent each gain control of all creatures the other controls until end of turn

This explains why the goblins remain unaffected

" —War blessing of Serra

If you search your library this way

Grunn, the Lonely King [Dominaria Prerelease Promos] Judge Gift Cards 2004 You and that opponent eachSet: Dominaria Prerelease Promos Type: Legendary Creature Ape Warrior Rarity: Uncommon Cost: {4}{G}{G} Kicker {3} (You may pay an additional {3} as you cast this spell.) If Grunn, the Lonely King was kicked, it enters the battlefield with five +1 +1 counters on it. Whenever Grunn attacks alone, double its power and toughness until end of turn.