The Goal of Pet Adventures is to get all 4 chests, not just beat the Boss. So in this game task, you need to work together with your other Guildmates to win 4 Chests, which will give you the chance to raid the completed map again later (within the the same day) when you start again. The chests themselves drop items for you to level up your pets, which you  need in other areas of the game to increase your success rates. Each map has a spot for 3 players, and each player needs to take 1 path each and stick to it in order to get the 4 chests at the end. Some maps are easier then others. the first 4 are considered the "obvious" given how easy the paths are.  The key to success is Communication and team work.
Click on images to enlarge and view the map.