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SCHG How-to

Fix Blue Knuckles

From Sonic Retro

(Original guide by Tamkis)

(Additional and optional steps by AlexShx)

Who is Blue Knuckles: the bug explained

Most people do not know, but in S3&K, there is a “hidden character” that is “unlockable” via Game Genie/Action Replay codes. This hidden character is Blue Knuckles. He is more than a palette change of the normal Red Knuckles; actually, he is identified internally as the character used for values greater than 3 for the variable player_mode. This variable, as the name states, determines what character(s) are in the game. The values are as follows:

  • #0. Sonic & Tails
  • #1. Sonic alone
  • #2. Tails alone
  • #3. Red Knuckles
  • #4+.Blue Knuckles

The problem with making Blue Knuckles a playable character, however, is that he is not blue in the Special Stages, and most of his level events fail to work. In the Special Stages, he transforms into Sonic (lol). These errors happen, because Sega, in the asm code of S3&K (sonic3k.asm), mostly used comparison statements such as this:

		cmpi.w		#3,(Player_mode).w
		bne.s		[label]


The label jumped to in statements like that would do something specific for when the player_mode is NOT 3 (Red Knuckles). Blue Knuckles is player_mode ID #4, so, with that statement, the game would goto the label meant for Sonic &/or Tails player modes, which is not what we want. We want Blue Knuckles to do the code after the bne.s, which is meant for Red Knuckles. This guide will fix statements of this format

The other comparison statement that is causing problems is in this format:

		cmpi.w		#3,(Player_mode).w	
		beq.s		[label]


If player_mode is #3 (Red Knuckles), the game will jump to a label for special processing for Knuckles events. If player_mode is NOT #3 (Red Knuckles), then the game will execute code for Sonic &/or Tails. Since Blue Knuckles (ID #4) is NOT ID #3, the game will execute Sonic &/or Tails code for Blue Knuckles, which is not what we want. We want Blue Knuckles to execute code for Red Knuckles. This guide will also fix statements of this format.


Making Blue Knuckles selectable

Save Screen

However, before we fix level events and other similar things for Blue Knuckles, let us make him a character that can be selected through ordinary means, without GG/AR codes. First, let us make him a selectable character in the Save Screen.

In the sonic3k.asm file in your S3&K .svn disasm, goto label SaveScreen_MainLoop / loc_C802 It should look something like this:

; loc_C802
SaveScreen_MainLoop:
		move.b	#$1E,(V_int_routine).w
		jsr	(Wait_VSync).l
		addq.w	#1,(Level_frame_counter).w
		jsr	(Process_Sprites).l
		move.w	(Camera_X_pos_copy).w,d0
		neg.w	d0
		move.w	d0,(H_scroll_buffer+2).w
		jsr	(Render_Sprites).l
		lea	(Normal_palette_line_3+$2).w,a0
		moveq	#$E,d0
		move.w	($FFFFE666).w,d1
		addq.w	#1,d1
		cmpi.w	#3,d1
		bcs.s	+
		moveq	#0,d1


Change this:

		addq.w	#1,d1
		cmpi.w	#3,d1


To this:

		addq.w	#1,d1
		cmpi.w	#4,d1    ; Blue Knuckles Fix: Now character #4 is the highest selectable


Then, goto label Obj_SaveScreen_NoSave_Slot / Obj_SaveScreen_D30C It should look something like this:

Obj_SaveScreen_NoSave_Slot:
		move.b	#$F,$1D(a0)
		move.w	($FFFFEF4C).w,d0
		addq.w	#3,d0
		move.b	d0,$22(a0)
		tst.b	($FFFFEF4B).w
		bne.s	loc_D396


Change this:

		addq.w	#3,d0


To this:

		addq.w	#4,d0    ; Blue Knuckles Fix: No Save Slot - Now character #4 is the highest selectable


Afterwards, go to subprgm sub_D6D0; it should look like this:

sub_D6D0:

		moveq	#0,d2
		tst.w	($FFFFB07A).w
		bne.s	loc_D6FA
		move.b	(Ctrl_1_pressed).w,d1
		lsr.w	#1,d1
		bcc.s	loc_D6EE
		moveq	#$5B,d2
		addq.w	#1,d0
		cmpi.w	#3,d0
		bls.s	loc_D6FA
		moveq	#0,d0
		bra.s	loc_D6FA
; ---------------------------------------------------------------------------


Change this:

		cmpi.w	#3,d0


To this:

		cmpi.w	#4,d0    ; Blue Knuckles Fix: Save Slot Update Character - Now character #4 is the highest selectable


Furthermore, goto label loc_D6EE. It should look like this:

loc_D6EE:
		lsr.w	#1,d1
		bcc.s	loc_D6FA
		moveq	#$5B,d2
		subq.w	#1,d0
		bpl.s	loc_D6FA
		moveq	#3,d0


Change this:

		moveq	#3,d0


To this:

		moveq	#4,d0    ; Blue Knuckles Fix: Save Slot Update Character - Reset character to #4 if below #0 (negative)


Those modifications changed the max player_mode for the Save Screen, from #3 (Red Knuckles) to #4 (Blue Knuckles). Note that Blue Knuckles’ picture in the Save screen shows part of the “Del” sign seen when deleting a save, instead of a picture of a blue Knuckles. You will have to repoint manually the art to a suitable picture for blue knuckles. Use SonMapED and modify General\Save Menu\Map - Save Screen General.asm

Level Select Screen

Next, we will fix the character select for the Level Select screen. This character selection is done by pressing C on the level select screen. Pressing C will increment the player_mode. As before, we will change the max character from #3 (Red Knuckles) to #4 (Blue Knuckles).

There is only on step to fix it here. Goto loc_7F46. It should look like this:

loc_7F46:
		btst	#5,(Ctrl_1_pressed).w
		beq.s	locret_7F60
		addq.w	#1,(Player_option).w
		cmpi.w	#4,(Player_option).w
		bcs.s	locret_7F60
		move.w	#0,(Player_option).w


Change this:

		cmpi.w	#4,(Player_option).w
		bcs.s	locret_7F60


To this:

		cmpi.w	#5,(Player_option).w   ; Blue Knuckles Fix: 04 is the highest selectable player_option
		blo.s	locret_7F60            ; Used mnemonic "blo" instead of "bcs" - if player_option is lower than 5 don't reset to 0

Note: you can make Blue Knuckles available only in the Level Select Screen.


Fixing bugs

Now that Blue Knuckles is available for selection by normal means, we still have to fix all of his level events and other bugs. To do so, we will have to fix the player_mode comparison statements that were shown before. Search for every instance of “cmpi.w #3, (player_mode).w”:

  • If the statement afterwards is “beq.s [label]”, change it to “bhs.s [label]”. (Branch if Higher or Same, the assembler will convert it to “bcc.s” when assembling)
  • If the statement afterwards is “bne.s [label]”, change it to “blo.s [label]”. (Branch if LOwer than, the assembler will convert it to “bcs.s” when assembling)


If you did all of the replacements correctly, all of the level events and most other things for Blue Knuckles will work. But wait! In replacing ALL of those conditional statements, you inadvertently made player #4 (Blue Knuckles) red and fixed the bugs that made him blue! The following steps will restore the bugs that made player #4 blue.

Goto the following labels and revert what you changed back to the original code (i.e. change “bhs.s [label]” to “beq.s [label]” and “blo.s [label]” to “bne.s [label]”),

The labels, and what reverting the code back does:

  • loc_61BE - Makes player #4 blue above water.
  • loc_7A18 - Makes player #4 blue underwater.
  • loc_8284 - Makes player #4 blue in Special Stages.
  • loc_55C84 - Makes player #4 blue when entering the pyramid after SOZ miniboss.


If you did that step and all of the other steps right, you should now be able to select Blue Knuckles from the Save and Level Select Screens. Most of the bugs involving Blue Knuckles should be fixed now too.


Additional step 1: Fix End of Level Signpost

Now, as soon as we can, we have to fix the end of level signpost graphic for Blue Knuckles. This is as easy as "weird".

Go to FrameArray_EndSign, change this:

FrameArray_EndSign:	dc.b	0,   0,	  1,   2


To this:

FrameArray_EndSign:	dc.b	0,   0,	  1,   2,   2,   2,   2,   2   ; Character shown per ID: 00 - Sonic, 01 - Sonic, 02 - Tails, 03 - Knuckles, 04to07 - Blue Knuckles (Knuckles with blue palette)


Done. This loads and displays the variant #2 of the End Signpost instead of a null one, and since Knuckles' palette is blue, the displayed character will be Blue Knuckles.


Additional step 2: Revert to blue palette after Super/Hyper Transformation

Ok, now we need to fix Super/Hyper Blue Knuckles reverting back in Red to his "normal form". This happens because he uses the "Red" Knuckles' palette transition when reverting back to "normal form".

Go to SuperHyper_PalCycle_Revert / loc_37EE:

It should look like this:

; loc_37EE:
SuperHyper_PalCycle_Revert:	; runs the fade in transition backwards
		cmpi.w	#2,(Player_mode).w	; If Tails or Knuckles, branch, making this code Sonic-specific
		bhs.s	SuperHyper_PalCycle_RevertNotSonic

		; run frame timer
		subq.b	#1,(Palette_timer).w
	...


Ok, now change this:

; loc_37EE:
SuperHyper_PalCycle_Revert:	; runs the fade in transition backwards
		cmpi.w	#2,(Player_mode).w	; If Tails or Knuckles, branch, making this code Sonic-specific
		bhs.s	SuperHyper_PalCycle_RevertNotSonic (loc_3820 in older disassemblies)

		; run frame timer


To this:

; loc_37EE:
SuperHyper_PalCycle_Revert:                          ; Runs the fade-in transition backwards
		cmpi.w	#4,(Player_mode).w                   ; Check if character is Blue Knuckles
		beq.s	SuperHyper_PalCycle_RevertSonic      ; If character is Blue Knuckles branch to Sonic's reverting palette transition
		cmpi.w	#2,(Player_mode).w                   ; If Tails or Knuckles, branch, making this code Sonic-specific
		bhs.s	SuperHyper_PalCycle_RevertNotSonic   ; (doesn't need to be changed as "Blue Knuckles' code" branched before)

SuperHyper_PalCycle_RevertSonic:                     ; Apply for Sonic and Blue Knuckles
		; run frame timer


Now Super/Hyper Blue Knuckles uses Super/Hyper Sonic's "reverting" transition wich makes him blue (and pretty) again after Super/Hyper form.


Unfixed bugs

Unfortunately Blue Knuckles has some bugs yet to be fixed:

  • He is messed up in the Slot Bonus Stage. See optional steps for hotfix
  • Blue Super/Hyper Knuckles turns Red, but at least reverts Blue. See optional steps for fast fix or complete fix

Optional steps

How to prevent Blue Knuckles from accessing the Slot Bonus Stage (hotfix)

This surely isn't the best way to do it, but in this case bugged is way worse than nothing.

Just go to loc_2D47E and change this:

loc_2D47E:
	...
		beq.s	loc_2D506
		move.b	#2,(Special_bonus_entry_flag).w
		move.w	#$1500,d1
	...


To this:

loc_2D47E:
	...
		beq.w	loc_2D506            ; (word used instead of short: jump distance too big)
		move.b	#2,(Special_bonus_entry_flag).w
		move.w	#$1500,d1            ; Load the Slot Bonus Stage
		cmpi.w	#4,(Player_mode).w   ; Check if player is Blue Knuckles 
		bne.s	.notBlueKnuckles     ; Skip if not Blue Knuckles
		move.w	#$1400,d1            ; Load Pachinko instead of Slot for Blue Knuckles

.notBlueKnuckles:
	...


As you see, this forces Blue Knux to enter Pachinko instead of Slot Bonus. You can use $1300 to load the Gumball Machine instead...or any stage or even code you want, at your own risk.


How to "Fix" Super/Hyper Blue Knuckles using Super/Hyper Sonic's palette cycles (fast fix)

In my case, since I don't want to make Super/Hyper Blue Knuckles appear like a "bad copy" of his famous red brother nor create a custom palette cycle, I figured out how to make his palette flash like Sonic's, fixing the "Blue Super/Hyper Knuckles turns Red" bug listed above in a cool and easy way.

Go to SuperHyper_PalCycle_Normal / loc_3854:

; loc_3854:
SuperHyper_PalCycle_Normal:
		cmpi.w	#2,(Player_mode).w		; If Tails...
		beq.w	SuperHyper_PalCycle_NormalTails
		cmpi.w	#3,(Player_mode).w		; ...or Knuckles, branch, making this code Sonic-specific
		bhs.w	SuperHyper_PalCycle_NormalKnuckles
		tst.b	(Super_Sonic_Knux_flag).w		; If Hyper Sonic, branch
		bmi.s	SuperHyper_PalCycle_HyperSonic


Ok, now revert "bhs.w" to "beq.w". Change this:

		bhs.w	SuperHyper_PalCycle_NormalKnuckles


To this:

		beq.w	SuperHyper_PalCycle_NormalKnuckles	; Super/Hyper Blue Knuckles now uses Super/Hyper Sonic's PalCycle (reverted Blue Knuckles Fix "bhs")

Note that this code changes only the color of Super/Hyper Blue Knuckles, this means that it doesn't add Hyper Sonic "Flashing Stars".


How to Fix Super/Hyper Blue Knuckles using a custom palette cycle

If you want Super/Hyper Blue Knuckles to be more "original" instead, you could create a different palette cycle for Super and Hyper Blue Knuckles by just messing around with the SuperHyper_PalCycle / SuperSonic_PalFlash subroutine, at label SuperHyper_PalCycle_NormalKnuckles / loc_393C.

The cycle that overrides palette on every frame is in that section and the palettes the code overwrites are at the bottom of the subroutine: you could just add a palette array by creating a copy of PalCycle_SuperHyperKnuckles / AnPal_SuperSonic_6, renaming it PalCycle_SuperHyperBlueKnuckles and editing every line to make Super/Hyper Blue Knuckles similar to "Super/Hyper Knuckles but blue"; just like this:

	...
PalCycle_SuperHyperKnucklesRevert:
		dc.w $64E,$20C,$206

; Super/Hyper Blue Knuckles cycle
PalCycle_SuperHyperBlueKnuckles:  ; New palette cycle for Super/Hyper Blue Knuckles
		dc.w $BGR,$BGR,$BGR       ; Frame 0
		dc.w $BGR,$BGR,$BGR       ; Frame 3
		dc.w $BGR,$BGR,$BGR       ; Frame 6
		dc.w $BGR,$BGR,$BGR       ; Frame 9
		dc.w $BGR,$BGR,$BGR       ; Frame C  - 12
		dc.w $BGR,$BGR,$BGR       ; Frame F  - 15
		dc.w $BGR,$BGR,$BGR       ; Frame 13 - 18
		dc.w $BGR,$BGR,$BGR       ; Frame 16 - 21
		dc.w $BGR,$BGR,$BGR       ; Frame 19 - 24
		dc.w $BGR,$BGR,$BGR       ; Frame 1C - 27


Make sure you replace every "BGR" with a valid Mega Drive palette color entry suitable for your Super/Hyper Blue Knuckles. Colors should be chosen wisely with PalCycle_SuperHyperKnuckles / AnPal_SuperSonic_6 taken as example.


Than just go to SuperHyper_PalCycle_NormalKnuckles / loc_393C and change this:

; loc_393C:
SuperHyper_PalCycle_NormalKnuckles:
	...
		; increment palette frame and update Knuckles' palette
		lea	(PalCycle_SuperHyperKnuckles).l,a0
		move.w	(Palette_frame).w,d0
	...


To this:

; loc_393C:
SuperHyper_PalCycle_NormalKnuckles:
	...
		; increment palette frame and update Knuckles' palette
		lea	(PalCycle_SuperHyperKnuckles).l,a0       ; Set to load Knuckles' palette cycle
		cmpi.w	#4,(Player_mode).w                   ; Check if player is Blue Knuckles
		bne.s	.notBlueKnuckles                     ; If not Blue Knuckles branch
		lea	(PalCycle_SuperHyperBlueKnuckles).l,a0   ; set to load Blue Knuckles' palette cycle

.notBlueKnuckles:                                    ; Apply selected palette cycle
		move.w	(Palette_frame).w,d0
	...


And finally, the last edit: this is mandatory if you don't want Blue Knuckles to briefly flash yellow before reverting to normal. Undo the reverting to blue step and go back to PalCycle_SuperHyperBlueKnuckles. Add this line under the palette array you just built:

PalCycle_SuperHyperBlueKnucklesRevert:   ; Restore original Blue knuckles' palette
		dc.w $E66,$C42,$822              ; Sonic's palette line, offset $4-$6-$8


Last step. Go to SuperHyper_PalCycle_RevertKnuckles. Change this:

SuperHyper_PalCycle_RevertKnuckles:
		lea	(PalCycle_SuperHyperKnucklesRevert).l,a0
		bra.w	SuperHyper_PalCycle_Apply


To this:

SuperHyper_PalCycle_RevertKnuckles:
		lea	(PalCycle_SuperHyperKnucklesRevert).l,a0       ; Set to load Knuckles normal colors
		cmpi.w	#4,(Player_mode).w                         ; Check if player is Blue Knuckles
		blo.s	.notBlueKnuckles                           ; If not Blue Knuckles (or character 4+) branch
		lea	(PalCycle_SuperHyperBlueKnucklesRevert).l,a0   ; Set to load Blue Knuckles normal colors (Sonic's palette line, offset $4-$6-$8)

.notBlueKnuckles:                                          ; Apply selected colors
		bra.w	SuperHyper_PalCycle_Apply


And there you have it! A true Super/Hyper form for our beloved Blue Knuckles.


(Anyways) Now you can enjoy your new “Character”!

SCHG How-To Guide: Sonic the Hedgehog 3 and Knuckles
Fixing Bugs
Fix Blue Knuckles | Fix Tails' Respawn Speeds | Fix Super Sonic Bugs
Design Choices
Fix Scattered Rings' Underwater Physics | Edit Level Select Text & Pointers | Work with Water
Adding Features
Restore (Sonic 2) Options Menu