1. Add a new "Extra Skill System" where killing monsters has a chance to drop skill books for heroes to learn new skills
2. Various "inheritance certificates" have been reduced from 9000 gold coins to 8000
3. Added a roaming mode (significantly increased monster value, increased chance of dropping items when killing monsters)
4. In "Roaming Mode", a specific NPC will appear, allowing the purchase of skill books
5. "Endless Mode" adds the "Endless Mage Contract", allowing the purchase of any skill book
