doc/nx2: Add world max unlock codes and information

doc/game/20-nx2.md

@@ -22,6 +22,132 @@ Freestyle, Nightmare
 Either take a look at the `missions.txt` file in the `game` data folder or use [Turkeyslam's guide](guide/nx2.pdf) which
 was published on ph-online back in the days. 
 
+### Missions.txt
+Take a look at the `missions.txt` file which should easily reveal a bunch of useful information already like mission
+conditions.
+
+### Turkeyslam's guide
+See [here](guide/nx2.pdf).
+
+### Unlocks sourced from disassembly (icex2)
+Sourced from the disassembly of the 1.54 build.
+
+Code format is mapped to numpad on a keyboard, e.g. down left = 1, down right = 3, center = 5, up left = 7, up right = 9
+
+#### Barriers
+* White: See [Ice Castle Codes](#ice-castle)
+* Red: Clear "Solitary 2 - Mir - Mirtain"
+* Yellow
+    * Clear mission "Canon-D [Full Song] - D - Barharn"
+    * Clear mission "Mine Zone 7 - Harena"
+* Light green (might be referred to as green)
+    * Clear mission "For You - Castle - Rootinia"
+    * Total worldmax progress >= 12%
+* Green (might be referred to as dark green)
+    * Clear mission "U Inside My Dim Memory [Full Song] - Castle 2 - Shantomia"  
+    * Clear mission "Witch Doctor #1 - Hidden Parts - Shantomia"
+* Sky blue: See [Ice Castle Codes](#ice-castle)
+* Blue: See [Mystery Box Codes](#mystery-box)
+* Violet: See [Mystery Box Codes](#mystery-box)
+* Pink 
+    * Unlock warp field in "Mirtain"
+    * Unlock warp field in "Barharn"
+* Grey
+    * Clear "Treme-Vook of the War - Factory - Morigin"
+    * At least 60% worldmax progress
+* Black: Play with USB profile
+* Dark yellow (might be referred to as orange)
+    * Unlock warp field in "Harena"
+    * Total worldmax progress >= 40%
+
+#### Mystery Box
+Per credit, you can enter a single code, only. Each code can only be entered once per profile.
+
+##### Song unlocks
+* ???: 15597553
+* So - Another: 55755595
+* Dance Vibrations - Another NM: 17933971
+
+##### Extra mileage
+* 200: 79797979
+* 300: 55555135
+* 400: 1311311131111
+* 500: 11597533
+* 600: 11997733
+* 600: 7993995991999
+* 700: 13391339
+* 1000: 5153595713795
+* 1000: 1751751751751
+
+##### Barrier unlocks
+* Violet: 3995557777555
+* Blue: 7911197333555
+
+#### Ice Castle
+To be able to enter these, you have to clear the mission "Ice Castle - Cryomiston". Once the mission is cleared,
+icicles appear on the various "Crystal" missions and the "B.P.M.". The following commands require you to start
+on a specific location and follow a path by entering the given pad commands. If the command is entered
+successfully, an animation will play.
+
+##### Barrier unlocks
+* White
+    * Move the mission marker on mission "Crystal S"
+    * Enter: 997711339713
+    * Path finishes on mission "Crystal S"
+* Sky blue
+    * Move the mission marker on mission "Crystal S"
+    * Enter: 977931139797
+    * Path finishes on mission "Ice Castle"
+
+##### Extra mileage
+* 300
+    * Move the mission marker on mission "Crystal S"
+    * Enter: 799317793117
+    * Path finishes on mission "Crystal S"
+* 400
+    * Move the mission marker on mission "Crystal S"
+    * Enter: 991773199131
+    * Path finishes on mission "Crystal S"
+* 500
+    * Move the mission marker on mission "Crystal W"
+    * Enter: 933779337711
+    * Path finishes on mission "Crystal W"
+* 500
+    * Move the mission marker on mission "Crystal WS"
+    * Enter: 991173379911
+    * Path finishes on mission "Crystal WS"
+* 600
+    * Move the mission marker on mission "B.P.M."
+    * Enter: 931793177931
+    * Path finishes on mission "B.P.M."
+* 700
+    * Move the mission marker on mission "Ice Castle"
+    * Enter: 113993117793
+    * Path finishes on mission "B.P.M."
+* 700
+    * Move the mission marker on mission "Crystal S"
+    * Enter: 799317793117
+    * Path finishes on mission "Crystal S"
+
+##### Song unlocks
+* Ugle Dee - Another FS
+    * Move the mission marker on mission "Crystal WS"
+    * Enter: 931793177993
+    * Path finishes on mission "Crystal EN"
+* ???
+    * Move the mission marker on mission "Crystal W"
+    * Enter: 939311799317
+    * Path finishes on mission "B.P.M."
+* ???
+    * Move the mission marker on mission "Crystal S"
+    * Enter: 917917919913
+    * Path finishes on mission "B.P.M."
+
+## Unlock and modifier codes
+All codes must be entered in the song select menu. When a code was entered successfully, a sound effect is played. An
+icon on the left/right side of the screen indicates if the modifier is active for player 1/2. These codes do not work
+on World Max (station).
+
 ### Cancel
 Clear all modifiers previously enabled.