There are several ways to use them, including minigames and contests, but none of those things are possible if you don't acquire them first, and acquiring monsters is what Carnival of Monsters is about
If you don't control an Army, create a 0/0 black Orc Army creature token first.) Creature - Warrior Orc Witch-king of Angmar Flying Whenever one or more creatures deal combat damage to you, each opponent sacrifices a creature of their choice that dealt combat damage to you this turn
Red Dragon Archfiend Deck 1 Bargain price reduction and layaway
This obviously gets worse the more EtB heavy opposing decks are (and the more they have high-end haymakers), but against most midrange decks and tokens decks itll do serious work, even buying you a turn where folks cant redeploy those bodies
All in all, it's hard to say if more monsters like this will ever be printed
5) Hops Zacian ex (128/100) The Secret Art Rares in Battle Partners are all desirable, but Hops Zacian is close to the top of the list, only falling behind a few other cards in value