During an Event, event monsters may appear on the map. There are two types of them.
You need to fight the first type of monsters or barter with them using event weapons. A portal to a treasury with three chests sometimes opens after the fight.
You can get Event Weapons:
- by exploring the event location,
- in event monster treasuries,
- by buying them in the Store with rubies.
The second type of monsters appear at various points on the map and give bonuses when you tap/click on them. Keep playing for these monsters to appear on the map again.