Event added in Season 5 Episode 4 and is done in the Map Swamp of Calmness and the intent is to kill the Medusa (Boss).
Only characters level 400 who have not done 3rd quest can enter the Swamp of Calmness. all you need to do to go is warp there when swamp event is indicated
Moving on to Swamp of Calmness will appear in the safe zone where there are 4 sites which send you to the hunting area.
You are able to Enter to Zone A,B,D Except C portal (Where Boss Can be Found). You will need to kill about 176 monsters Within the areas Then Zone C will open, Head there find Medusa (Boss) and kill her befor the time runs out