This lovely little loop relies on a perpetual motion machine of mutual blinking. When you cast Felidar Guardian, its entry trigger targets Icewind Stalwart, whisking it away and bringing it right back. That fresh arrival from Icewind Stalwart triggers its own protection fighting style, instantly returning the favor by exiling and returning Felidar Guardian to the battlefield. Because both enter-the-battlefield abilities can continuously target one another without running out of eligible non-Warrior targets, you get an endless cascade of creature entries and leaves.