Ancient Coin
A coin minted in ancient times.
Etc. Items
Sell Price to Secret Vendors: 50 
Gold
Sell Price at Black Trader: 10K-30K Gold
How to Obtain:
Opening:
Gift Box
Event Boxes
Used:
Trade Ancient Coin (3) to 
Rafril/Ratas (NPC) (located next to respective spawns at the beach) for experience and 1,000 or 800 Gold (alternates between giving 1,000 and 800). Experience given is equal to your character's level multiplied by 50.
Notes:
Ancient Coins can be found as low as 5K during event box drops, but can potentially rise up to 25K in absence of event box drops. Used primarily to level up at higher levels.