Mastery Bonus Options have 2 options:
In Set items: Damage Decrease (25-50-75)
In Weapons: Increase all stats (10-25-40)
You obtain Mysterious stone from exchange Jewel of Excel at NPC "Moss" in Loreancia.
You can obtain Mastery option from:
- Chaos combination
- Mysterious stone
When upgrading ruud set and weapon, you have a chance that Mastery option will disappear.