118.5a
A spell whose mana cost is {0} must still be cast the same way as one with a cost greater than zero; it won’t cast itself automatically. The same is true for an activated ability whose cost is {0}.
A spell whose mana cost is {0} must still be cast the same way as one with a cost greater than zero; it won’t cast itself automatically. The same is true for an activated ability whose cost is {0}.