Skill Advancement system was added in level 70 patch (patch 80 in March 2019). Skill Advancement is added to tab in skill menu (key K). This unlocks on level 66.

For each level above 65, you can improve one skill. You occasionally receive skill advancement XP as reward of Vanguard Requests, killing level 66+ monsters in the open world or while fishing. Enough XP gives one Skill Advancement point. You can spend points to upgrade existing skills.

Skills to improve unlock at level 66, 68, 70. Skill can be upgraded up to 60 times (maximum of 180 points). Advancing skill takes 1 point and initially 3000 gold and 28 Advancement Scroll I. Advancing skill also raises character power, crit factor or endurance (up to 20 each). At level 67 and level 69 you can activate optional effects for a skill.

This should be the number of scrolls needed to maximize a skill:

  • Lvl 66: 2141 Skill Advancement Scroll I
  • Lvl 67: 240 Skill Optimization Scroll I for each skill to unlock ×3
  • Lvl 68: 3483 Skill Advancement Scroll II
  • Lvl 69: 300 Skill Optimization Scroll II each ×3
  • Lvl 70: 4701 Skill Advancement Scroll III

Originally, to fully maximize one character you needed 1,600,335Gold coin.[1] Each of three skill option unlocks at level 67 costs 50,000Gold coin, and on level 68 65,000Gold coin, and Skill Optimization Scrolls but no Skill Advancement points. In later patches cost was halved. Alternative is to buy Serghetto Box I. This gives scrolls to update first skill without paying more gold. As of January 2021 patch v102 box is also available from Development Merchants. Buying 20 boxes (~80000 gold) should have level 66 skill maxed, and possibly some scrolls for higher skills. You still need to grind Skill Advancement Scrolls. In patch 108 in August 2021 Skill Advancement basically became free if you grind long enough, since new Skill Advancement Stone token gives Skill Advancement Books to advance without paying gold and Complete Skill Advancement Books, which do not require even scrolls.

Skill Advancement Scrolls are guest rewards from green daily quests or dungeon Vanguard rewards or dungeon drops. Scrolls have three tiers and can be converted to higher level scrolls:

  • 7x Skill Advancement Scroll I -> 1x Skill Advancement Scroll III
  • 7x Skill Advancement Scroll II -> 1x Skill Advancement Scroll III
  • 3x Skill Optimization Scroll I -> 1x Skill Advancement Scroll III
  • 3x Skill Optimization Scroll II -> 1x Skill Advancement Scroll III

Outside events getting scrolls is long and tedious task, and upgrading skills costly. Getting Skill Advancement XP and points is now easier and faster with Azart Hatchery special dungeon. In later patches getting skill XP is trivial, since any dungeon run gives several points.