nessa pokemon card full art - 118/100 (118/100) RarityUltra Rare Card TypeTrainer FormSupporter Nessa - 157/185 (Reverse Foil)

Jawbone Duelist Toxic and double strike is a combo of abilities begging you to be creative

There are narrow exceptions where a judge may issue a proxy during an event if a card is accidentally damaged, but thats not the same thing as bringing your own proxies

As for the Mythic Invitational itself, I would call the event a modest success

After you move your venture marker into the last room of a dungeon and that room's ability resolves (or otherwise leaves the stack), the dungeon leaves the game and you have now completed it

Craterhoof Behemoth is the gold standard, but pretty much any of these effects are good