All purchases add more.
A mighty and dark sorcerer used the Ancient Jewel to open the forgotten Gates of Despair.Then he split the Jewel into four separate pieces and gave these pieces to four mystical creatures so no one will ever be able to use the Jewel to close the Gates.
You have to destroy those creatures and collect all of the pieces to close the Gate of Despair forever! Slash and slice the evil creatures until they die and drop their coin. Collect coin and use it to upgrade.