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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 &c. 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

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

Afterwards, goto 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

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

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

To this:

	cmpi.w	#5,(Player_option).w

Fixing bugs

Now that Blue Knuckles is now 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 “bcc.s [label]”. If the statement afterwards is “bne.s [label]”, change it to “bcs.s [label]”.

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 “bcc.s [label]” to “beq.s [label]”. i.e. change “bcs.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

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", fixing it is easy:

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		; (loc_3820 in older disassemblies)

; SuperHyper_PalCycle_RevertSonic:
		; run frame timer
		subq.b	#1,(Palette_timer).w		; ($FFFFF65E in older disassemblies)
		bpl.s	locret_37EC
		move.b	#3,(Palette_timer).w		; ($FFFFF65E in older disassemblies)

		; decrement palette frame and update Sonic's palette
		lea	(PalCycle_SuperSonic).l,a0
		move.w	(Palette_frame).w,d0		; ($FFFFF65C in older disassemblies)
		subq.w	#6,(Palette_frame).w	; previous frame		; ($FFFFF65C in older disassemblies)
		bhs.s	loc_381E		; branch, if it isn't the first frame
		; The following line should be a move.w
		; This causes the fade-in to be bugged
		move.b	#0,(Palette_frame).w		; ($FFFFF65C in older disassemblies)
		move.b	#0,(Super_Hyper_palette_status).w	; 0 = off		; ($FFFFF65F in older disassemblies)

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

; SuperHyper_PalCycle_RevertSonic:
		; run frame timer
		subq.b	#1,(Palette_timer).w
		bpl.s	locret_37EC
		move.b	#3,(Palette_timer).w

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 charachter 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	; loc_3820 (doesn't need to be changed as "Blue Knuckles' code" branched before)

SuperHyper_PalCycle_RevertSonic:		; Removing the semicolon makes "SuperHyper_PalCycle_RevertSonic" a label
		; run frame timer
		subq.b	#1,(Palette_timer).w
		bpl.s	locret_37EC
		move.b	#3,(Palette_timer).w

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

There are some bugs that I am still trying to fix with Blue Knuckles

  • He is messed up in the Slot Bonus Stage.
  • Blue Super/Hyper Knuckles turns Red (but reverts Blue - Additional step)
  • There is no end-of-level sign for Blue Knuckles (the top half disappears when the results appear).

Optional step

How to "Fix" Super / Hyper Blue Knuckles using Super / Hyper Sonic's palette cycle

Since I don't want to make Super / Hyper Blue Knuckles appear like a "bad copy" of his famous red brother I figured out how to make his palette flash like Sonic's, "fixing" the "Blue Super/Hyper Knuckles turns Red" bug listed above.

Fixing is very very simple. 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
		bcc.w	SuperHyper_PalCycle_NormalKnuckles			; "Blue Knuckles Fix": "beq.w" to "bcc.w" (fixed before)
		tst.b	(Super_Sonic_Knux_flag).w	; If Hyper Sonic, branch
		bmi.s	SuperHyper_PalCycle_HyperSonic

Ok, now revert "bcc.w" in "beq.w": change this:

		bcc.w	SuperHyper_PalCycle_NormalKnuckles			; "Blue Knuckles Fix": "beq.w" to "bcc.w" (fixed before)

To this:

		beq.w	SuperHyper_PalCycle_NormalKnuckles			; Super / Hyper Blue Knuckles now uses Super / Hyper Sonic's PalCycle

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


(Anyways) Enjoy your new “Character”!