What are the official rulings for Walking Ballista?

The official rulings for Walking Ballista state that it enters the battlefield with a number of 1/1 counters equal to the amount of mana spent to cast it. It can be tapped to put a 1/1 counter on itself, and it can also be tapped to deal damage to any target equal to the number of 1/1 counters on it. If it has 0 toughness, it will be put into the graveyard as a state-based action.