Season 12 (2016-2017) is the fourth class change. Part 1 opened Nixies Lake with the boss Nix, added the Labyrinth of Dimensions and the Dark Angel weapon and Holy Angel armour tiers. Part 2 raised the level cap to 920, added the 4th class quest at NPC Sent, the skill enhancement tree with its debuff and explosion skills, the five-floor Deep Dungeon, around 200 guide quests and the Jewel Bingo minigame.
The 4th class change

Sent, a Guardian Knight of Lugard, came to Lorencia at Priest Devin's request to test the heroes of MU and pass on her techniques. Talking to her moves you to the Space of Qualification, where you can form a party; from there one member applies and the whole party moves into the Space of Trial. You need level 750 to enter and level 800 to finish the chain. Progress is saved, so you can leave and resume at the stage you reached.
| Stage | Objective | Reward |
|---|---|---|
| 1. Test of Qualification | Sent appears in person — bring her HP to 0, then talk to her | 20 stat points |
| 2. New Battle (1) | Kill 5 each of the Deep Dungeon Skeleton Warrior, Cyclops and Ghost, and survive 5 minutes against endless spawns | 30 stat points |
| 3. New Battle (2) | Fight Sent again — this time she uses extra skills and casts far more often | 50 stat points, the Ashen Scroll of Oblivion, the 4th class change and the skill enhancement tree |
The quest runs on the character who accepted it, and only party members at the same stage complete it with you. The scroll arrives through the Gremory Case and is held for 7 days. In total the chain pays 100 stat points.

| Base class | 3rd class | 4th class |
|---|---|---|
| Dark Knight | Blade Master | Dragon Knight |
| Dark Wizard | Grand Master | Soul Wizard |
| Elf | High Elf | Noble Elf |
| Summoner | Dimension Master | Dimension Summoner |
| Magic Gladiator | Duel Master | Magic Knight |
| Dark Lord | Lord Emperor | Empire Lord |
| Rage Fighter | Fist Master | Fist Blazer |
| Grow Lancer | Mirage Lancer | Shining Lancer |
Skill enhancement tree, debuffs and explosion skills

Finishing the 4th class change unlocks the skill enhancement tree, opened with Ctrl + A or from the character window. You gain 1 point per level and spend it on the tree. Each class has a fixed list of main skills that can be enhanced, and the enhanced version replaces the original skill. Skill enhancement options (damage, hit count, attack speed and range, splash damage, extra targets, cooldown reduction, weapon attack or wizardry power) apply only to the main skill they are attached to.
Debuffs
The tree also buys debuff options, which land on the target at the enhanced chance. Enhancing the basic option applies the basic debuff; the upgrade option upgrades it while the basic debuff is still running. All four debuffs can sit on a target at once. At launch they worked on monsters only.
| Line | Basic debuff | Upgraded debuff | Explosion skill | Effect when it fires |
|---|---|---|---|---|
| Poison | Venom | Intoxication | Poison Storm | Explodes the intoxication and spreads venom to monsters around the target |
| Freeze | Frost | Frozen | Frozen Slayer | Explodes the freeze and deals splash damage around the target |
| Bleed | Bleeding | Heavy bleeding | Bleeding Hit | Explodes the bleed and cuts the target's defense for a while |
| Shock | Shock | Stun | Stun Boom | Explodes the stun and blinds the target for 2 seconds |
Each explosion skill needs the upgraded debuff on the target and removes it when used — after which the debuff can be applied again. The MU Helper was extended to match: explosion skills cannot go in the basic skill slot, but both trigger skill slots accept them, and the trigger conditions moved into a single settings popup.
Level 920, new experience rules and attack speed caps
The level cap moved to 920. A third-class character stops earning experience at level 800 and only starts earning again after the 4th class change, and fourth-class characters gain experience only from monsters of monster level 160 or higher. The new experience table is applied at the moment of the class change, so characters already above 800 may see their level shift slightly — level 810 typically becomes 813 to 815, for example.
Damage now also depends on the gap between your level and the monster's. If your character level is above the monster level + 600, both your damage and the damage you take apply at 100%. Below that the difference costs you: roughly 10% per level of reduced attack damage and increased damage taken, capped at 70%. It applies to normal, elemental and debuff damage alike.
| Class | Maximum attack speed |
|---|---|
| Dark Knight | 288 |
| Dark Wizard | 284 |
| Elf | 275 |
| Summoner | 188 |
| Dark Lord | 450 |
| Magic Gladiator | 351 |
| Rage Fighter | 441 |
| Grow Lancer | 273 |
Attack speed is now hard-capped per class — buffs and items stop helping once you reach the number — and the character window shows it as current / maximum.
Nixies Lake

Nixies Lake was the most beautiful lake on the continent until Selupan's blizzard destroyed it and killed the spirit Nixie; her brother Nix turned into an evil spirit and now rules the frozen lake. Entry needs level 700, either through the gate in Raklion at (210, 218) or from the move command window for 50,000 zen. The monsters here drop excellent Holy Angel armour.

| Monster | HP | Attack | Defense | Elemental attack | Elemental defense | Attack speed |
|---|---|---|---|---|---|---|
| Paraka | 240,000 | 2,500–2,550 | 1,800 | 930–1,110 | 1,500 | 1,000 |
| Beth | 120,000 | 1,500–1,600 | 1,400 | 960–990 | 1,500 | 800 |
| Vaski | 125,000 | 3,100–3,200 | 1,500 | 1,200–1,300 | 1,500 | 2,000 |
| Nix (boss) | 30,000,000 | — | — | — | — | — |
The Nix boss fight

The boss zone needs a Fragment of Spirit Nixie, bought from Priest James's Ruud shop (Elbeland 32, 239 or the Event Map Plaza 216, 55). Every member of a party needs one. Click the frozen Spirit Nixie at Nixies Lake (113, 109) and the fragment is consumed as you enter.
Once someone is inside, the door shuts and no one else can join; party members who die cannot come back in. After the kill you may stay 5 minutes before being moved to the safe zone at (24, 118), and the boss drops one item per character present when it dies.

| Skill | What it does |
|---|---|
| Energy Sphere | Throws an energy sphere; high chance of a 30 second attack and defense debuff. |
| Ice Rain | Rains ice around itself; low chance of a 30 second freeze. |
| Ice Breath | Sprays a long line of ice straight ahead; being hit slows you for 1 minute. |
| Ice Boom | Follows Ice Breath — a circle appears under the target and fills with ice shards after 2 seconds. |
| Knowledge Absorption | At HP thresholds Nix becomes invulnerable for 3 minutes and raises 2 barrier stones while spamming Ice Rain. Fail to break them in time and 20 Nixies Lake monsters spawn. Barrier stones take only elemental damage. |
| Devil Ice | The ultimate: magic circles appear at random spots, and 10 seconds later black ice falls everywhere except on the circles. Being caught sets your HP to 0. |
| HP recovery | If nobody is in range for 4 seconds, Nix heals every second. |
Deep Dungeon

The Deep Dungeon is the levelling ground for the new cap. Entry needs level 770, on foot through the Lorencia entrance at (177, 31) or from the move command window. All five floors drop jewels, normal and excellent equipment, excellent Holy Angel armour and elemental items; rings appear from floor 3 and necklaces from floor 4.
| Floor | Recommended level | Monsters | Monster level |
|---|---|---|---|
| 1 | 770 – 800 | Skeleton Warrior, Larva, Cyclops | 170 |
| 2 | 801 – 830 | Cyclops, Ghost, Skeleton Archer | 200 |
| 3 | 831 – 860 | Skeleton Archer, Hell Hound, Hell Spider | 230 |
| 4 | 861 – 890 | Hell Spider, Skeleton Warrior Captain, Thunder Lich | 260 |
| 5 | 891 – 920 | Thunder Lich, Poison Bull Fighter, Dark Knight, Gorgon | 290 (Gorgon 300) |
Labyrinth of Dimensions
Elena's warped dimension became a solo dungeon. Enter through the Gate of Dimension at the Event Map Plaza (236, 58) — solo only, master level and above, and you need at least 10 stamina. The labyrinth resets every Thursday 8:00–10:00, and anyone still inside at 08:00 is thrown out.
It runs over 7 stages. Each stage is a set of disconnected rooms, arranged randomly, that you cross through gates: normal rooms are empty, special rooms spawn 4–8 endlessly respawning monsters and assign one mission (the gate only appears once it is done), and the exit room assigns five missions that clear the stage.
| Mission types |
|---|
| Kill a target number of monsters |
| Collect a target amount of zen |
| Reach a target cumulative damage dealt |
| Reach a target amount of experience |
| Reach a target cumulative damage taken |
| Reach a target Helper usage time |
| Kill a target number of monsters without healing potions |
| Kill a target number of monsters without mana potions |
| Stage | Ruud | Extra reward |
|---|---|---|
| 1 | 150 | — |
| 2 | 200 | Jewels of Bless |
| 3 | 450 | Jewels of Bless |
| 4 | 800 | Jewels of Bless |
| 5 | 1,550 | Jewels of Bless |
| 6 | 1,850 | Jewels of Bless |
| 7 | 2,000 | Jewels of Bless |
Rewards arrive in the Gremory Case and are held for 7 days; the number of Jewels of Bless scales with how many monsters you killed. Entries reset at the weekly maintenance and you start again from stage 1. Labyrinth monsters drop only zen, town portal scrolls do not work inside, and only rooms you have visited appear on the minimap.
Dark Angel weapons and Holy Angel armour
Season 12 stacked two more tiers on top of Blood Angel. Both upgrades are 100% and run at the Chaos Goblin in Noria (180, 103).
| Upgrade | Base item | Key material | Jewels | Result |
|---|---|---|---|---|
| Blood Angel weapon → Dark Angel weapon | +11 with +16 additional damage | Anvil of Dark Angel (Ruud, Priest James) | 30× Bless +2, 30× Soul +2, Jewel of Chaos, Jewel of Creation | Dark Angel weapon at +0, keeping its excellent options and Luck |
| Dark Angel armour → Holy Angel armour | +11 with +16 additional defense | Soul of Holy Angel (Ruud, Priest James) | 30× Bless +2, 30× Soul +2, Jewel of Chaos, Jewel of Creation | Holy Angel armour at +0, keeping its set stat option and Luck |
Dark Angel weapons require level 600 and carry excellent damage rate +10%, attack or wizardry +45, attack speed +7, +1.6 attack per 20 levels and life and mana recovery on kills.
| Dark Angel weapon | Class | Attack power | Speed | Req. STR / AGI |
|---|---|---|---|---|
| Dark Angel Sword | Blade Master | 354–365 | 40 | 935 / 303 |
| Dark Angel Magic Sword | Duel Master | 351–361 (70%) | 45 | 419 / 149 |
| Dark Angel Staff | Grand Master, Duel Master | 143–149 (102%) | 30 | 208 / 97 |
| Dark Angel Bow | High Elf | 375–395 | 45 | 192 / 1,118 |
| Dark Angel Stick | Dimension Master | 133–139 (100%) | 30 | 341 / 103 |
| Dark Angel Scepter | Lord Emperor | 262–272 (pet 68%) | 40 | 408 / 147 |
| Dark Angel Claw | Fist Master | 252–262 | 35 | 547 / 186 |
| Dark Angel Lance | Mirage Lancer | 178–188 | 40 | 418 / 297 |
Holy Angel armour requires level 800 and pushes the mastery set bonuses to their highest values yet. Excellent Holy Angel pieces drop from Nixies Lake and the Deep Dungeon.
| Pieces | Holy Angel set bonus |
|---|---|
| 2 set | Skill attack power +35 (+50 for wizard sets) and the main stat option +90 |
| 3 set | Double damage rate +18% and attack power +100 (wizardry +100 for wizard sets) |
| 4 set | All stats +20, base defense +40 (+60 wizard, +35 fighter and lancer), critical damage +40, excellent damage +70, critical damage rate +20%, excellent damage rate +20%, ignore enemy defense 9% |
Two combination materials were also renamed: the Soul of Ancient Hero became the Soul of Blood Angel, and the Fragment of Sealed Stone became the Soul of Dark Angel.
Dual-class mastery gear, quivers and Ruud
Energy elves and wizard-type magic gladiators finally got mastery sets of their own, sold sealed by Priest James for 30,000 Ruud a piece. Conversion scrolls move an existing set between builds at 100% at the Chaos Goblin, keeping the item's level and options.
| Conversion scroll | Turns | Price |
|---|---|---|
| Support-type Elf scroll | Attack elf set → support elf set | 10,000 Ruud |
| Attack-type Elf scroll | Support elf set → attack elf set | 30,000 Ruud |
| Wizard-type MG scroll | Knight MG set → wizard MG set | 10,000 Ruud |
| Knight-type MG scroll | Wizard MG set → knight MG set | 30,000 Ruud |
Quivers
Bows and crossbows became one-handed: the bow goes in the left equip slot and a quiver in the right. A quiver is an enhanceable off-hand that takes Luck and additional damage, upgrades from +0 to +15, comes in normal, excellent, socket and mastery versions, and lets bows fire without consuming arrows. Its attack power and speed count only while a bow or crossbow is equipped.
| Quiver | Attack power | Speed | Req. STR / AGI | Where |
|---|---|---|---|---|
| Battle Quiver | 111–137 | 50 | 62 / 172 | Sold by Elder Garus in Noria; excellent version drops from level 77–95 monsters |
| Devilwood Quiver | 181–207 | 55 | 149 / 851 | Drops from Selupan |
| Blood Angel Quiver | 283–310 | 55 | 177 / 1,049 | Priest James |
| Dark Angel Quiver | 341–366 | 55 | 186 / 1,107 | Second mastery weapon crafting |
Because both hands now hold socket items, the total socket count across them is capped at 6 — a 5-socket weapon leaves room for a 1-socket quiver only. To help, the Seed Master in Elbeland (46, 243) gained a socket slot reduction combination: an empty 4- or 5-socket item plus a Jewel of Creation, a Jewel of Chaos and 1,000,000 zen becomes a 3-socket item at 100%, keeping level, skill, Luck and options. Socket bows and crossbows now drop with 1 to 3 sockets.
Two more changes: a Dark Spirit can be kept in the inventory and activated by right-clicking, like the Dark Horse; and Ruud was redenominated — 1 Ruud became 100 Ruud, with every price and payout rescaled to match.
Master skill tree renewal

With debuffs moving to the new tree, the debuff-flavoured master skills were pulled out. Every class lost Increase Poison / Lightning / Ice Resistance and Strong Will, and a set of chance-based nodes changed from 1 point to 10 points per rank while their cap rose from 3.34% to 4.17%: Vengeance, double damage, ignore defense, excellent damage, critical damage, full mana recovery, full life recovery and full SD recovery.
Per class, the stun and slow masteries were removed and replaced with straight damage or utility. The Blade Master, for instance, lost Twisting Slash Mastery, Rageful Blow Mastery, Death Stab Proficiency and Mastery, Blow Mastery and both Iron Defense nodes; Blow Proficiency became a plain damage increase, Combo Strengthener moved from rank 8 to rank 7, and a new Max Life Amplification node was added at rank 7. A bug where some master skills gained nothing from a grade upgrade was also fixed.
Guide quests, Jewel Bingo and other changes
About 200 guide quests were added on their own tab in the quest window. They are accepted automatically as you reach the level for them, one at a time, and you claim the reward by clicking the quest window — no NPC needed. They ask you to travel somewhere, collect items, kill monsters, reach a level or finish another quest, and an Instant Move button teleports you to the map and walks you to the objective. Abandoning a quest immediately accepts the next one and the abandoned one is gone for good; a whole chapter can be switched off with the checkbox next to its title.

Jewel Bingo works like Mine Finder: collect 24 card pieces while hunting (tick "event item" in the Helper) to make a card bundle. Place your jewels on the board or use auto-place, choose a box, then click the jewel on your board matching each one the box calls. Lines across, down or diagonally score a bingo, lines through the MU in the centre are worth more, and the game ends when the box runs out. The reward box depends on your score and lands in the Gremory Case (K), where it lasts 1 day.
Event maps rebanded
| Tier | Chaos Castle / Blood Castle / Devil Square / Doppelganger | Mastery Boxes |
|---|---|---|
| 1 | 50 – 199 | — |
| 2 | 200 – 299 | — |
| 3 | 300 – 399 | — |
| 4 | 400 – 549 | 1 |
| 5 | 550 – 649 | 2 |
| 6 | 650 – 769 | 2 |
| 7 | 770 + | 2 |
Illusion Temple moved to five bands (180–299, 300–399, 400–599, 600–769, 770+) and pays 2 boxes from tier 3 up; the Imperial Guardian fortress also pays 2. The Ruud inside low, mid and high mastery boxes was reduced, and event map monsters were rebalanced to match the new bands.
Smaller changes: map movement levels were unified for first and second class characters (Dungeon 3 50→40, Atlans 70→60, Lost Tower 4 and 5 60→50); reconnecting in Feria, Nars or Nixies Lake puts you in the safe zone; unread mail now shows an icon that opens the mailbox; the login, character and friend windows were redrawn; and the move command window gained a favourites list of up to five destinations.
- 4th class change quest at NPC Sent
- Level cap 920 and the skill enhancement tree
- Debuffs and explosion skills
- Nixies Lake and the boss Nix
- Deep Dungeon floors 1-5
- Dark Angel weapons & Holy Angel armour