The Pneumatic Spear is an upgrade for the standard Spear Gun. It can only be purchased from Earl at his house in WaterPort once the Spear Gun has reached a level of 10. More details on the conversion rate can be seen below. As it is an upgrade, it will convert the existing Spear Gun into the Pneumatic variation, i.e. it is only possible to have one or the other, not both types of Spear Gun.