You can equip up to three amulets before heading into battle. There are 10 different kinds and while you have one slot for free, the other two amulet slots cost 30 rubies each. These amulets can be upgraded up to three times, and you'll unlock the majority of amulets by reaching different levels. Few types of amulets:
Potion Upgrade: Attack and block potion timer now 10 seconds.
XP Bonus: XP earnings plus 10 percent.
Special Damage: Special attack damage plus 10 percent.
Glorious Strike: Glorious Strike stun of 3.5 seconds.
Bleed: Each successful attack makes the enemy bleed five damage per second.