Beast Taming by the World: I Synthesize While Others Upgrading

One day, the city underwent a drastic change. The entire city passed through to another world. When the communication was cut off, all the people in the city received the hint of a system. With the summon book, everyone can summon different creatures. Therefore, people took their summoning creatures to take risks outside the city and found that as long as they killed a creature, they would have the chance to turn it into the summoning thing of the summon book! However, when Ethan woke up from the hangover, he found that the creatures sealed in his summon book can be used to synthesize higher price creatures. An ordinary goblin turned into a powerful goblin mutant! The drastic change brought crisis and opportunities to the city. How did Ethan and his best friend become the new rule-makers of the city?