This loops hinges on Selvala, Heart of the Wilds producing massive mana through its tap ability, which is then fueled further by the passive power boost from Frostcliff Siege to ensure X remains high. Once you have that mana flowing, you use Temur Sabertooth's activation to bounce Selvala back to your hand and immediately recast her, generating infinite enters-the-battlefield triggers. Each time Selvala re-enters, her own triggered ability even gives you opportunities to draw cards if her power outclasses the rest of your board.