What would you do if you were in a fight with a monster and then it begged you for mercy. What would you do ?

Depends on the context. My general attitude would be to be merciful, but it depends on other factors. Do I believe the monster is genuinely asking for mercy, or is this just a ruse? Is the monster too dangerous to be allowed to live even if it is genuinely asking for mercy? Did the monster do something for which there can be no forgiveness? Are there potential consequences for not granting mercy?