As long as it's your turn, Cait, Cage Brawler has indestructible (Effects that say "destroy" don't destroy that permanent. An indestructible creature can't be destroyed by damage.). Whenever Cait attacks, you and defending player each draw a card, then discard a card. Put two +1/+1 counters on Cait if you discarded the card with the highest mana value among those cards or tied for highest.