Dual Blade Skill Book Location

i can confirm final cut10 and chains of hell 10 drop from zak, i got both already for my DB.

idk about others ;x

Those skills max out at 30 right away after using the book.

Anyways, here's a speculated list, all of it needs confirmation:

Slash storm 20: Dodo, rex, stone golem
Tornado spin 20: Blue wyvern, rex
Flying assaulter 20: Griffey, memory monk trainee, skelegon
Mirror image 30: Memory monk, papulatus, rex
Venom 30: ? (same as regular?)
Final cut: Zakum, chaos zakum
Monster bomb 30: Qualm guardian, zakum, chaos zakum
Sudden raid 30: Lyka, horntail
Chains of hell: zakum, chaos zakum
Stack effect 30: Oblivion guardian
Thorns 30: Horntail