During the event, players can go to find NPC [Monster Battle Envoy] in Snow City / Azure City to enter the appointed event scene.  All of monsters in the scene take along with plenty of treasures or Core of Life.  After you collected enough Core of Life, you can exchange a BOSS shapeshift card from NPC Monster Battle Envoy.  

What's more, you may rob rare items from opposed players as well.  Let's shapeshift to BOSS and fight against those monsters now!

Treasure Chest