Heard this in the Vesteria Discord and thought that I could bring this idea to light and maybe delve into how this could work.
Ratty Ambush would be a raid for lower level players (20-30) similar to the Gauntlet. The player would complete the Rat King quest, then talk to the former Rat King. The player would speak with the former Rat King and he would explain that he does love rats but there has been an overpopulation issue, he would ask for your help clearing out the sewers.
You would accept and delve into a giant Sewer pipe, Humanoid Rat Mutants and regular Rats set up territory in this giant pipe building a sort of civilization. You would begin to slay the Rats, they would have a 60% chance to drop a Rat Claw or a Rat Eye. which could be used as a currency to buy cosmetics that the rat king would buy off of you for various items (Headgear Def scroll, Ratty mask/Helmet.
You could accept this quest once per hour considering the drop rate of the Rat Claw/ Rat Eye reducing it being too easy to farm.
Glad I could bring this idea to life and delve into it. Have a great day