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SCHG How-to

Add Extra Characters To Sonic 2

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Revision as of 11:53, 14 July 2013 by ThomasSpeedrunner (talk | contribs) (Went on a grammar nazi spree and rewrote a lot of parts since they rendered the guide unusable.)

(Guide By Manic Remix)

(Revised by ThomasSpeedrunner)

I was very surprised that this guide didn't exist anywhere else. It seems like nowadays this is the what everybody has in their hacks. This guide will show you how to add extra characters to Sonic The Hedgehog 2 (16-bit). We will use the SVN disassembly. In this guide, I will refer to Knuckles, and Amy.

First, open up s2.asm. Search for "Obj_Index:".

You will see this or something like it: <asm> 

       dc.l Obj01	; Sonic

dc.l Obj02 ; Tails dc.l Obj03 ; Collision plane/layer switcher dc.l Obj04 ; Surface of the water dc.l Obj05 ; Tails' tails dc.l Obj06 ; Rotating cylinder in MTZ, twisting spiral pathway in EHZ dc.l Obj07 ; Oil in OOZ dc.l Obj08 ; Water splash in Aquatic Ruin Zone, Spindash dust dc.l Obj09 ; Sonic in Special Stage dc.l Obj0A ; Small bubbles from Sonic's face while underwater... </asm>

And it will go on. Now, search for "dc.l ObjNull". Replace <asm> dc.l ObjNull ; Obj4C dc.l ObjNull ; Obj4D </asm> 

with

<asm>ObjPtr_Knuckles: dc.l Obj4C ; Knuckles ObjPtr_Amy: dc.l Obj4D ; Amy </asm>

You've now created an "Knuckles", and "Amy" object. These are the object IDs that will be used for new characters.

Next, search for "InitPlayers:". You will see this or something like it: <asm> 

       InitPlayers_TailsAlone:

move.b #ObjID_Tails,(MainCharacter).w; load Obj02 Tails object at $FFFFB000 move.b #ObjID_SpindashDust,(Tails_Dust).w; load Obj08 Tails' spindash dust/splash object at $FFFFD100 addi.w #4,(MainCharacter+y_pos).w rts </asm>

Now, below: <asm> InitPlayers_TailsAlone </asm>

add <asm> subq.w #1,d0 bne.s InitPlayers_KnuxAlone ; branch if this is a Knuckles alone game </asm>

Now, below the "rts", add <asm>InitPlayers_KnuxAlone: subq.w #1,d0 bne.s InitPlayers_AmyAlone ; branch if this is an Amy alone game move.b #ObjID_Knuckles,(MainCharacter+id).w move.b #ObjID_SpindashDust,(Sonic_Dust+id).w rts

InitPlayers_AmyAlone: move.b #ObjID_Amy,(MainCharacter+id).w move.b #ObjID_SpindashDust,(Sonic_Dust+id).w rts </asm>

Now, go to s2.constants.asm. Find this line: <asm>ObjID_Buzzer = id(ObjPtr_Buzzer) ; 4B </asm> And insert this under it: <asm>ObjID_Knuckles = id(ObjPtr_Knuckles) ; 4C ObjID_Amy = id(ObjPtr_Amy) ; 4D </asm>

Next, go to "OptionScreen_Choices:", and find this line: <asm> dc.l (3-1)<<24|(Player_option&$FFFFFF) </asm> Change the 3 to a 5. This will allow for Knuckles and Amy player options. Now go here: <asm>off_92D2: dc.l TextOptScr_SonicAndMiles dc.l TextOptScr_SonicAlone dc.l TextOptScr_MilesAlone </asm> And add this under it: <asm> dc.l TextOptScr_KnuxAlone dc.l TextOptScr_AmyAlone

Now, head here: <asm>off_92DE: dc.l TextOptScr_SonicAndTails dc.l TextOptScr_SonicAlone dc.l TextOptScr_TailsAlone </asm> Add the same two lines as before under: <asm> dc.l TextOptScr_TailsAlone </asm>

Now find this: <asm>TextOptScr_TailsAlone: menutxt "TAILS ALONE " ; byte_981C: </asm> And add this below it: <asm>TextOptScr_KnuxAlone: menutxt "KNUCKLES ALONE " TextOptScr_AmyAlone: menutxt "AMY ALONE " </asm>

Congratulations! You have two new characters. Now you will need to make new sprites, palette, and code for them to work. A good start would be to copy and paste Sonic's code into a new ASM file and change the labels so you don't get "symbol double defined" errors. Have a great day.

SCHG How-To Guide: Sonic the Hedgehog 2 (16-bit)
Fixing Bugs
Fix Demo Playback | Fix a Race Condition with Pattern Load Cues | Fix Super Sonic Bugs | Use Correct Height When Roll Jumping | Fix Jump Height Bug When Exiting Water | Fix Screen Boundary Spin Dash Bug | Correct Drowning Bugs | Fix Camera Y Position for Tails | Fix Tails Subanimation Error | Fix Tails' Respawn Speeds | Fix Accidental Deletion of Scattered Rings | Fix Ring Timers | Fix Rexon Crash | Fix Monitor Collision Bug | Fix EHZ Deformation Bug | Correct CPZ Boss Attack Behavior | Fix Bug in ARZ Boss Arrow's Platform Behavior | Fix ARZ Boss Walking on Air Glitch | Fix ARZ Boss Sprite Behavior | Fix Multiple CNZ Boss Bugs | Fix HTZ Background Scrolling Mountains | Fix OOZ Launcher Speed Up Glitch | Fix DEZ Giant Mech Collision Glitch | Fix Boss Deconstruction Behavior | Fix Speed Bugs | Fix 14 Continues Cheat | Fix Debug Mode Crash | Fix 99+ Lives | Fix Sonic 2's Sega Screen
Design Choices
Remove the Air Speed Cap | Disable Floor Collision While Dying | Modify Super Sonic Transformation Methods & Behavior | Enable/Disable Tails in Certain Levels | Collide with Water After Being Hurt | Retain Rings When Returning at a Star Post | Improve the Fade In\Fade Out Progression Routines | Fix Scattered Rings' Underwater Physics | Insert LZ Water Ripple Effect | Restore Lost CPZ Boss Feature | Prevent SCZ Tornado Spin Dash Death | Improve ObjectMove Subroutines | Port S3K Rings Manager | Port S3K Object Manager | Port S3K Priority Manager | Edit Level Order with ASM‎ | Alter Ring Requirements in Special Stages | Make Special Stage Characters Use Normal DPLCs | Speed Up Ring Loss Process | Change spike behaviour in Sonic 2
Adding Features
Create Insta-kill and High Jump Monitors | Create Clone and Special Stage Monitors | Port Knuckles
Sound Features
Expand Music Index to Start at $00 | Port Sonic 1 Sound Driver | Port Sonic 2 Clone Driver | Port Sonic 3 Sound Driver | Port Flamewing's Sonic 3 & Knuckles Sound Driver | Expand the Music Index to Start at $00 (Sonic 2 Clone Driver Version) | Play Different Songs Per Act
Extending the Game
Extend the Level Index Past $10 | Extend the Level Select | Extend Water Tables | Add Extra Characters | Free Up 2 Universal SSTs
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