In short
- Up to +3 is guaranteed. +3 to +12: 66%. +12 to +16: 55%. +16 to +20, weapons only: 40%.
- No item ever breaks: a failure drops it back to the floor of its band.
- Premium does not touch any chance.
No hidden number and no surprise. Nothing breaks, and premium does not touch any chance.
Each band has its own chance and its own fallback:
In week 1 nobody goes past +12, whatever is in the account or in the wallet. It rises to +16 in week 4, and +20 on weapons only exists from week 8, when the Ancestral Scroll arrives. And when you hit that limit, the game tells you what the ceiling is now and which week it rises, instead of just refusing and leaving you thinking it is broken.
Not enchant chance, not drop chance, not experience, not an extra window. It is three things and no more: 25% more adena, 25% more Seal, and 2 more hours of autofarm a day. Somebody paying plays at the same x500 as everybody else, and reaching 85 hands you 7 free days of it through the catch-up bonus.