The collector is helping those who have completed their tasks. 
If you collected the 3 Golden Roses (given by Collector in May), give it to him so that he makes your Winged Harpy base level: 190

This Quest is available until June, 04

The Current formula for Neo WingedHarpy is: 
Winged Harpy (3rd stage mix item) + Worm (3rd stage mix item)

Worm can be obtained by completing the Quest Made of Alchemy, in Pirate Island.