%w.att,? Total Damage % ? huh?

1. Total dmg% is the % derive from the damage range, example i had weapon that add 9% total dmg, my max atk range is 1000, after the effect, my max atk range will be 1090. (can be stack)
Yes, it works like that, the stacking, though, is not yet concretely confirmed. %damage surely stacks with %luk, %atk, whether or how it stacks with another %damage is not known. Words have it that it doesn't self-stack.

2. attack %, derive from total base weapen atk (include atk pot and atk apple, but not include bullet and star), (can be stack)
Yes, it works like that. Not sure about stacking, though most likely it stacks with other additions multiplicatively, self-stack additionally.

3. stat %, derive from the total stat after base stat+ mw stat. (can be stack)
((Base*MW) + EquipBonus) * %stat
Stacks with other potential % bonuses multiplicatively, stacks with other %stat bonuses additionally.

4. boss dmg %, add up on skill %, example a skill deal 280% dmg, after this stat --> 280% + 30% = 310% dmg on boss. (cannot be stack)
Same as 1. Doesn't stack, fo sho.
If you do 100k hit, with 30% boss damage, it becomes 130k.


question about potential skill:

1. how many skill is provided on potential system?
Decent Haste, Door, Hyper Body, and Sharp Eyes, so 4.

2. does each of the skill only available for certain rank of the EQ? (rare, epic, unique)
All skills can only be obtained on Unique equipment.

Sorry for double post, I meant to copypaste and edit.