Costumes

Costumes are basically a second set of gear that you can build. Each piece give strength agility intelligence and wisdom. You can get costume pieces from a lot of things in game but most will come from costume packs from the roulette and buying pieces with vouchers. You can upgrade these costume pieces by synthesizing other costume pieces for the same slot into the one you want to keep. When you synthesize these pieces together there is a chance that you will receive additional costume effects, and it's the only way to get fantasy costume pieces. When you synthesize them together there is also a random chance that the costume piece will become permanent. Any piece of costume gear can become permanent this way.

I found that it was easiest for me to make them permanent was to save a couple of the angel/devil packs from the roulette and then open them all at once and put them together. Then I started one piece at a time buying them from the voucher store and making them permanent. Don't worry if one expires on you, just save it. When you get the next one you can put the expired one in it and get all the levels on the new piece.

Any piece of costume gear you level up has a chance of spawning the fantasy costume pieces which are what would be considered your epic costume pieces. The important thing is getting a piece in each slot and making it permanent.