someone know what can buy from Credit(s)
Use your credits to transfer your character to other servers during server transfer time.
or you can give them to someone to transfer. (but only during transfer event time - and you just missed the last one; we usually have 2 transfer events each year)
I use to only use my credits for the level 5 drill stone... the problem is there is no way to gift the items bought with credits so when you no longer need the low level items the credits just pile up.