According to a post by CM Seraphina Brennan, these special costumes have been live in Korea for a while now and have been in demand in the west. The new system will use “in-game methods” to level, including crafting.
“As the base costume levels up, it will gain additional stats. In the initial ranks, the pool of possible stats it will draw from will be very limited,” Brennan writes. “But what’s important here is that the base costume is leveled up and made more powerful by in-game item drops and in-game crafting.”
The improved costume synthesis system is coming this month along with the hard mode for Mistsong Summit. The team is currently testing a new skill queue and promised that server transfers will return by the end of the month.