This quest can be missed!!
After defeating Medusa, go to Pendrago church, you should see Mayvin and a priest talking. After Marvin go, the priest will give you something to deliver.
First, go to Gaferis Ruins, talk with the guards on the entrance. They will tell you that Mayvin has gone to Great Camelot Bridge.
After clearing 4 trials, go to Great Camelot Bridge Central Camp and talk to a merchant there (with “!” on his head). He will tell you that Mayvin has gone to Ganglen Ruins.
Go there and you will find Mayvin. He’s on B1, and you should see “!” on Ganglen Ruins B1 (located on the entrance from Westronbolt Gorge). Mayvin will give you the reward (Fluffy Repede).
You need to clear this quest before the 2nd meeting with Lion (lord) of calamity!! The reward is only a fashion item, but it’s quite good :).