Last updated: July 23, 2026

On this page: The 4th Class · Skill Enhancement Tree · Nixies Lake · Boss Nix · Labyrinth of Dimensions · Darkangel & Holyangel Gear · Deep Dungeon · Everything Else · FAQ

MU Online Season 12 – The 4th Class, Nixies Lake & Deep Dungeon

Season 12 (2016–17) is the biggest character milestone since Season 3: the 4th class change arrived, with its own quest, skill tree and golden regalia. Around it grew a new endgame — Nixies Lake, the Labyrinth of Dimensions, the Deep Dungeon — and the mastery ladder climbed to Darkangel weapons and Holyangel armor. From the original patch notes with the original artwork.

The 4th Class Change

The lore: after Crywolf's defense, apostle Devin summons Cent — Lugard's guardian knight and fellow member of the twelve — to test MU's heroes. Speak to NPC Cent in Lorencia (131,147) to enter the Space of Qualification and pass her trial:

3rd class	→ 4th class	3rd class	→ 4th class
Blade Master	Dragon Knight	Lord Emperor	Empire Lord
Grand Master	Soul Wizard	Dimension Master	Dimension Summoner
High Elf	Noble Elf	Fist Master	Fist Blazer
Duel Master	Magic Knight	Mirage Lancer	Shining Lancer

The Skill Enhancement Tree

Completing the quest unlocks a fifth progression system (Ctrl+A or the character window button): 1 point per level after the 4th change, spent on per-class skill strengtheners — Dragon Knights sharpen Rageful Blow and Fire Blow lines, Soul Wizards their Meteor and Evil Spirit families, Noble Elves Multi-Shot and Focus Shot, and so on through all eight classes. Alongside it, the old master tree was renewed: resistance and anti-stun debuff nodes removed, new skills added, and broken rank scalings fixed.

Nixies Lake

Nixies Lake — element zones around the boss area	The Dimensional Gate in the Event Map Square

The most beautiful lake of the continent, blessed by the spirit siblings Nixie and Nix — found by the descendants of the great wizards hunting the Secromicon spellbook. Entry at level 700+ through Raklion (210,218) or the move window (50,000 zen); one internal gate (66,114 ↔ 145,95). Its monsters drop excellent Holyangel armor:

Paraka — the corrupted lakedweller	The lake's trident guard	The frost mage of the shore	Nix — the boss of the frozen depths

The Nix Boss Zone

Rule	Details
Ticket	Spirit Nixie's Fragment — Ruud shop (James: Elbeland 32,238 / Event Square 216,55); every party member needs one
Entry	Click the frozen Spirit Nixie at (113,109) — the fragment is consumed
Boss-zone lock	No entry until Nix has spawned; the door seals once a group is inside; the dead cannot re-enter; the zone closes 5 minutes after the kill
Why	Nix drops the era's top loot — and the fight's ice AoEs made elemental defense mandatory

Labyrinth of Dimensions

Elena's broken dimension, rebuilt over years into a maze her allies now ask heroes to purge. Solo-only, master level required, entered through the Dimensional Gate at the Event Map Square (236,58). Cleared zone by zone against Kundun's trapped forces for one of the era's biggest Ruud incomes — with a full reset every Thursday 08:00–10:00 (characters inside get evicted at 8). The weekly Ruud routine was born here.

Darkangel Weapons & Holyangel Armor

The mastery ladder grew both directions — weapons caught up with armor, and armor climbed a tier:

DA Sword (DK)	DA Magic Sword (MK)	DA Staff (SW)	DA Bow (Noble Elf)
DA Stick (DS)	DA Scepter (Empire Lord)	DA Claws (Fist Blazer)	DA Lance (Shining Lancer)

Craft (Noria Chaos Goblin)	Recipe
Darkangel weapon	Bloodangel weapon +11 with +16 attack + Darkangel Anvil (Ruud shop) + Bless bundle +2 (30) + Soul bundle +2 (30) + Chaos + Creation
Holyangel armor	Darkangel set piece +11 with +16 defense + Holyangel Soul (Ruud shop) + the same jewel suite — enhancement resets, but set stat options and Luck survive

Holyangel armor	The gold-and-white tier	Winged helms	The red capes

The same update reworked Ruud payouts and added the energy elf's own mastery sets — Bloodangel/Darkangel/Holyangel Elf lines with buff-strengthening set options (defense/attack enhance +7–16%), finally making support elves first-class mastery citizens.

Deep Dungeon

Floor 1 — recommended 770–800	Floor 5 — the bottom

Five floors under Lorencia (entrance 177,31), for levels 770+, each floor a ~30-level band with elemental Skeleton Warriors, Larvae and Cyclopes. Drops run from jewels through excellent Holyangel and element items — the classic "dungeon" reborn as endgame, slotting into the route right after Ferea.

Everything Else in Season 12

Update	Details
Guide quests	The "Hero's Growth" quest journal: chained objectives (kill counts, map visits) with exp/zen rewards — MU finally got a quest tracker
Jewel Bingo	The third minigame: fill bingo lines with mined jewels for stacking rewards — joins MU Rummy and Find the Bomb
Play improvements	Helper polish, stat window rework showing specialization detail, event inventory — the QoL pass of the era
Master tree renewal	Debuff/resistance nodes cut, new actives added, rank scaling bugs fixed — trees got leaner and stronger

Continue Reading

Guide	Why it helps
Season 11 guide	Ferea and Darkangel armor, right before.
Classes overview	All the 4th classes in today's roster.
Ruud guide	The mastery ladder in its modern form.
Master skill tree	The renewed trees explained.
Leveling guide	Where Nixies and Deep Dungeon fit the route.

FAQ

Where can I play Season 12?
Browse the Season 12 private servers listed — the 4th class ships in every later version too.

What level should I be for the 4th class quest?
It targets endgame masters — realistically ML400+ characters; Cent's trial scales to hurt.

Is the Labyrinth worth running weekly?
Yes — it was the single best Ruud-per-hour source of the era, which is why the Thursday reset became a calendar event.

Do I need Holyangel before the 4th class?
No — they are parallel tracks. Most players quest at Darkangel and upgrade to Holyangel from Nixies drops afterward.