MU Online – Complete Timeline (2001–2025)
| Year | Version | Event Type | Description | Region | Language| Reverse Insight |
|----------|---------------|-----------------|-------------------------------------------------|--------|---------|-------------------------------------------------|
| 2001 | Version 74 | Pre-Season | Basic MMORPG gameplay; level up, fight monsters | Korea | Korean | Earliest internal alpha builds, no event logic |
| 2002 | Version 97 | Pre-Season | Devil Square, Blood Castle, wings level 1–2 | Korea | Korean | Client versions 0.97d and 0.99b appear in forums|
| 2003 | Version 99 | Pre-Season | Dark Lord class, Chaos Castle, item +13 | Korea | Korean | SQL dumps contain only basic tables |
| 2004 | Season 0 | Castle Siege Dev| CastleSiege.doc authored internally | Korea | Korean | MapServerInfo.dat in early EMUs |
| 2005 | Season 0 | Castle Siege Rel| Castle Siege goes live | Korea | Korean | EventServer handshake modularized |
| 2006 | Season 1 | Patch Note | Crywolf, Castle Siege, Ancient items, Fenrir | Korea | Korean | CrywolfEvent.txt leaks with KR comments |
| 2006 | Season 2 | Patch Note | Kanturu, Jewel of Harmony, SD system, Aida | Korea | Korean | Early socket item logic emerges |
| 2008 | Season 3 Ep1 | Patch Note | L3 wings, Illusion Temple PvP | Korea | Korean | Seed Sphere via DLL hooks |
| 2008 | Season 3 Ep2 | Patch Note | Skill Tree, Summoner, UI updates | Korea | Korean | Opcode mismatch in leaked skill tree |
| 2009 | Season 4 | Patch Note | La Cleon, Raklion, Vulcanus, Moss Merchant | Korea | Korean | Socket system formalized |
| 2010 | Season 5 | Patch Note | Gens, Fortress Imperial, +15 items | Korea | Korean | Faction PvP logic in EMUs |
| 2010 | Season 6 P1 | Patch Note | Rage Fighter, small wings, MU Helper | Korea | Korean | Skill pkt headers 0xC1/0xF3 |
| 2011 | Season 6 P3 | Global Release | Global MU Online S6-3 (Dec 21, 2011) | Global | English | EMU forks align to Webzen release |
| 2012 | Ex700 | Patch Note | Elemental system, cap raised | Korea | Korean | Elemental resistance reversed |
| 2013 | Season 8 | Patch Note | Debenter, mining, cap 730 | Korea | Korean | Mining logic in client DLLs |
| 2014 | Season 9 | Patch Note | Urk Mountain, Lord Silvester, Pentagrams | Korea | Korean | MUUN upgrade logic patched |
| 2015–2020| Season 10–16 | Patch Note | Grow Lancer, Rune Mage, Guardian system | Korea | Korean | DX9+ client breaks old EMUs |
| 2021–2023| Season 17–19 | Patch Note | Kanturu Underground, Atlans Abyss, Companions | Global | English | Commercial forks mimic Webzen logic |
| 2024 | Season 20 | Patch Note | Abyssal Temple, Alchemist, Ethereal weapons | Global | English | IGCN suite includes partial logic |
| 2025 | Season 21 | Patch Note | Infinity Tower, PvP rebalance, guild fortress | Global | English | EMU forks reflect S21 mechanics |
| Year | Version | Event Type | Description | Region | Language| Reverse Insight |
|----------|---------------|-----------------|-------------------------------------------------|--------|---------|-------------------------------------------------|
| 2001 | Version 74 | Pre-Season | Basic MMORPG gameplay; level up, fight monsters | Korea | Korean | Earliest internal alpha builds, no event logic |
| 2002 | Version 97 | Pre-Season | Devil Square, Blood Castle, wings level 1–2 | Korea | Korean | Client versions 0.97d and 0.99b appear in forums|
| 2003 | Version 99 | Pre-Season | Dark Lord class, Chaos Castle, item +13 | Korea | Korean | SQL dumps contain only basic tables |
| 2004 | Season 0 | Castle Siege Dev| CastleSiege.doc authored internally | Korea | Korean | MapServerInfo.dat in early EMUs |
| 2005 | Season 0 | Castle Siege Rel| Castle Siege goes live | Korea | Korean | EventServer handshake modularized |
| 2006 | Season 1 | Patch Note | Crywolf, Castle Siege, Ancient items, Fenrir | Korea | Korean | CrywolfEvent.txt leaks with KR comments |
| 2006 | Season 2 | Patch Note | Kanturu, Jewel of Harmony, SD system, Aida | Korea | Korean | Early socket item logic emerges |
| 2008 | Season 3 Ep1 | Patch Note | L3 wings, Illusion Temple PvP | Korea | Korean | Seed Sphere via DLL hooks |
| 2008 | Season 3 Ep2 | Patch Note | Skill Tree, Summoner, UI updates | Korea | Korean | Opcode mismatch in leaked skill tree |
| 2009 | Season 4 | Patch Note | La Cleon, Raklion, Vulcanus, Moss Merchant | Korea | Korean | Socket system formalized |
| 2010 | Season 5 | Patch Note | Gens, Fortress Imperial, +15 items | Korea | Korean | Faction PvP logic in EMUs |
| 2010 | Season 6 P1 | Patch Note | Rage Fighter, small wings, MU Helper | Korea | Korean | Skill pkt headers 0xC1/0xF3 |
| 2011 | Season 6 P3 | Global Release | Global MU Online S6-3 (Dec 21, 2011) | Global | English | EMU forks align to Webzen release |
| 2012 | Ex700 | Patch Note | Elemental system, cap raised | Korea | Korean | Elemental resistance reversed |
| 2013 | Season 8 | Patch Note | Debenter, mining, cap 730 | Korea | Korean | Mining logic in client DLLs |
| 2014 | Season 9 | Patch Note | Urk Mountain, Lord Silvester, Pentagrams | Korea | Korean | MUUN upgrade logic patched |
| 2015–2020| Season 10–16 | Patch Note | Grow Lancer, Rune Mage, Guardian system | Korea | Korean | DX9+ client breaks old EMUs |
| 2021–2023| Season 17–19 | Patch Note | Kanturu Underground, Atlans Abyss, Companions | Global | English | Commercial forks mimic Webzen logic |
| 2024 | Season 20 | Patch Note | Abyssal Temple, Alchemist, Ethereal weapons | Global | English | IGCN suite includes partial logic |
| 2025 | Season 21 | Patch Note | Infinity Tower, PvP rebalance, guild fortress | Global | English | EMU forks reflect S21 mechanics |