SCHG How-to

Fix DEZ Eggrobo boss collision glitch

From Sonic Retro

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(Original guide by Flamewing)

In Death Egg Zone, the final boss you fight is the infamous Giant Mech. While cited for its difficulty, it is also known for a particularly annoying bug that makes the boss fight that much more difficult. When hitting the boss in a certain manner, (this is better described by flamewing) it can cause you to fall into the robot, being killed by its arms, instead of rebounding much in the manner that you would when fighting any other boss. In the Sonic 2 Heroes forum topic, flamewing discusses how exactly to fix it, and it is far simpler than many people believed.

Open up s2.asm and find label 'loc_3DFF8' or 'ObjC7_CheckHit'; this function is responsible for checking if:

1. If Eggrobo has been defeated: causes him to break up if so;

2. Otherwise:

1. If Eggrobo is flashing from a previous hit: keep flashing until timer runs out;

2. Otherwise:

1. If Eggrobo was hit on the body: play hit sound, start flashing;

2. Otherwise, if Eggrobo was hit on the head, then subtract 1 hit from hit counter, remove collision from body and proceed as previous item.

If you paid attention, you will have noticed that hitting Eggrobo in the head removes collision from the body, but that hitting him on the body does not remove collision from the head; we will fix this now. The easiest fix is to go to this piece of code:

 	move.b	#$3C,objoff_2A(a0)
 	move.w	#SndID_BossHit,d0
 	jsr	(PlaySound).l

and change it to this:

 	movea.w    objoff_36(a0),a1 ; a1=Eggrobo's head
 	clr.b    collision_flags(a1)	; Remove collision from head
 	move.b	#$3C,objoff_2A(a0)
 	move.w	#SndID_BossHit,d0
 	jsr	(PlaySound).l
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

|Fix DEZ Eggrobo boss collision glitch]]