To pull off this infinite loop, you first need to grant your Walking Ballista lifelink so that its damage-dealing ability also keeps your health pool topped up. Once that lifelink is online, you can fire off its activated ability to ping any target for 1 damage by removing a +1/+1 counter. That burst of lifegain immediately awakens Spider-Man, Peter Parker, whose triggered ability answers back by placing a fresh +1/+1 counter right back onto the Walking Ballista—netting you infinite damage, infinite lifegain triggers, and infinite life all at once.