The Rare Egg Machine is the main place for players to spend 
Magic Stones in order to obtain new and more powerful cards. The standard Rare Egg Machine costs five Magic Stones; however, special Rare Egg Machines may come up that can cost more.
Tip
Cards obtained from the REM should be favorited and saved, not sold or fused into other cards. GungHo buffs these cards all the time, and such buffs have made once worthless cards extremely valuable.