You will need small sphered glass cases & a jar of decaying flesh. Cast a charm at the stinksap. Cast spells in a sequence so that one layers on top of the other. The spells are to refill the stinksap once it is used. The Gobstone would be able to shoot with precision. Rules were to put in place to activate it & how it collected the magical ability. Assemble the glass case for the stinksap. Cast Incendio to create heat on the glass. As the glass melts, use your wand to spin the glass into a marble ball. Cast another spell to cool it down & use some spells to protect the Gobstone from breaking. Use the Switching Spell to switch the air to the stinksap inside the glass cases. Cast a spel onto the Gobstone to shield it from spells hitting it. If the Firing Charm fails when casting, close your mouth so that the stinksap won't be your next taste test.