Sonic the Hedgehog 2 (Nick Arcade prototype)/Technical information

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Art

Nemesis Compressed art locations

Offset	Description
$9DF8E	Shield
$9E114	Invincibility stars
$A0960	SEGA logo
$A1520	Title Screen graphics
$A2E82	Sonic & Tails at the Title Screen
$A39C6	GHZ bit of flower (S1)
$A3A10	GHZ & MZ platform with chain (S1)
$A3B2A	EHZ Log bridge
$A3C16	Unused 16x16 block (S1)
$A3C5E	GHZ rolling ball (S1)
$A3DFC	GHZ rolling log with spikes (S1)
$A4010	GHZ unused spikes around the rolling log (S1)
$A413C	GHZ rock (S1)
$A426A	GHZ breakable wall (S1)
$A4308	Some GHZ wall (S1)
$A4368	Unknown fire
$A44A0	Unused, possible burning log
$A45AE	Waterfall
$A46B4	Unused HTZ fireballs
$A4802	GHZ Log bridge (S1)
$A48DA	HTZ crossing platform
$A4BCE	HTZ automatic door
$A4C46	HTZ seesaw with green ball
$A4DDE	HPZ bridge
$A4F56	HPZ waterfalls
$A52B8	HPZ big emerald
$A552A	HPZ ledge artwork
$A55EA	HPZ glowing orb
$A5826	Some platform
$A59C0	Unknown unused dust
$A5AE0	CPZ floating platform
$A5C2E	Water surface
$A5D9E	Button
$A5E76	Vertical spring
$A5F92	Horizontal spring
$A605C	Diagonal springs
$A6230	Score/Rings/Time HUD
$A6338	Lives HUD
$A644E	Rings
$A6542	Monitors
$A696C	Vertical spikes
$A69BC	Gathered points
$A6A96	Prototype checkpoint
$A6B3C	Prototype end of level sign
$A6F8A	Crocodile
$A732C	EHZ Buzz Bomber
$A7512	HPZ Bat
$A7868	OOZ Octopus
$A7B88	Triceratops
$A7F84	HPZ Dinobot
$A835A	Unused sideways piranha
$A8852	OOZ Prototype seahorses
$A8CA0	Unused rolling ball
$A8F36	Unused Mother Bubbler
$A9162	Unused Bubbler
$A9384	EHZ Snail
$A9580	Prototype Crawler
$A9902	EHZ Piranha
$A9B0E	Boss ship
$AA24A	CPZ Prototype boss
$AA7A8	Big explosion
$AAE30	Robotnik's ship boost
$AAEAE	Puff of smoke
$AAF94	EHZ Boss
$AB780	EHZ Boss helicopter blades
$AB874	SBZ Ball Hog (S1)
$ABC34	Crabmeat
$AC122	GHZ Buzz Bomber (S1)
$AC4C8	Possible unknown explosion from the ground
$AC6B0	LZ Burrobot (S1)
$ACD9A	GHZ Piranha (S1)
$AD002	LZ Jaws (S1)
$AD28C	SYZ Roller (S1)
$AD7B0	GHZ Motobug (S1)
$ADA3A	GHZ Newtron (S1)
$AE058	SYZ Snail (S1)
$AE440	MZ Bat (S1)
$AE73C	Splats (S1)
$AE984	SLZ Bomb (S1)
$AEC1C	LZ Orbinaut (S1)
$AEDFA	MZ Catakiller (S1)
$AEF88	Title card (S1)
$AF596	Explosions
$AFBFC	GAME OVER, TIME OVER
$AFD8E	Vertical spring
$AFE90	Sideways spring
$AFF6C	Big ring flash
$B00E0	End of level hidden bonuses (S1)
$B03E2	Sonic at Continue screen + Continue star (S1)
$B0692	CONTINUE + Minisonic (S1)
$B08CC	Bunny
$B0A24	Chicken
$B0B80	Penguin
$B0CFC	Seal
$B0E18	Pig
$B0F4E	Flicky
$B1088	Squirrel
$B2184	EHZ graphics
$B5784	HTZ graphics
$B6BAA	HTZ placeholders for animated tiles
$C0492	HPZ graphics
$C31A0	HPZ glowing orbs
$CC8F4	CPZ graphics
$CFDC0	Unknown
$D8C34	GHZ graphics (S1)
$DC1F0	GHZ graphics (S1)
$E0B62	Ending scene additional graphics (S1)
$E0DEA	Credits font (S1)
$E13E8	SONIC THE HEDGEHOG ending text (S1)

Palette editing

These are the ROM offsets of the palettes:

Offset	Description
$245A	SEGA Foreground
$25A2	SEGA Background
$2622	Title Screen
$26A2	Level Select
$2722	Sonic and Tails
$2742	Green Hill Zone
$27A2	Hidden Palace Zone Underwater
$2822	Chemical Plant Zone
$2840	???
$2882	Emerald Hill Zone
$28E2	Hidden Palace Zone
$2942	Hill Top Zone
$29A2	(Sonic again?) (Maybe the special stage Sonic)
$2A22	Labyrinth Zone
$2A82	Scrap Brain Zone Act 3
$2B02	Labyrinth Zone Sonic Underwater
$2B22	Scrap Brain Zone Act 3 Sonic Underwater
$2B42	Special Stage Title Card (S1)
$2BC2	Continue - Sonic (S1)
$2BE2	Continue (S1)
$2C02	Sonic - Ending (S1)

Pattern load requests

PLRs are what load all the peices of art into the VRAM that are not in the main level load block. Here's a breakdown of the pattern load cue's in the S2 Alpha ROM:

00	1C09C	Standard block 1 (checkpoint/HUD/life counter/ring/gathered points)	(4)
01	1C0BC	Standard block 2 (Monitor/Shield/Invincibility stars)	(2)
02	1C0D0	Unknown (explosion)	(0)
03	1C0D8	Game/time over (game/time over text)	(0)
04	1C0E0	GHZ (GHZ patterns/GHZ Piranha/Vertical spikes/Vertical spring/Horrizontal spring/EHZ Log bridge/GHZ swinging platform/Motobug/GHZ Rock)	(8)
05	1C118	GHZ (GHZ Piranha)	(0)
06	1C120	LZ (CPZ DUPLICATE)	(2)
07	1C134	LZ (CPZ DUPLICATE)	(3)
08	1C120	CPZ (CPZ graphics/Unknown/floating platform)	(2)
09	1C134	CPZ (Vertical spikes/Diagonal springs/Vertical spring/Horizontal spring)	(3)
0A	1C14E	EHZ (EHZ graphics/Fireball/Waterfall/GHZ bridge/HTZ seesaw/Vertical spikes/Diagonal springs/Vertical spring/Horizontal spring)	(8)
0B	1C186	EHZ (Shield/Gathered points/Buzz Bomber/EHZ Snail/EHZ Piranha)	(4)
0C	1C1A6	HPZ (HPZ graphics/HPZ bridge/waterfall/platform/pulsing ball/HPZ stuff/master emerald/Water surface)	(7)
0D	1C1D8	HPZ (HPZ Dinobot/HPZ Bat/Crocodile/Buzz Bomber/HPZ Bat/Triceratops/Dinobot/Sideways piranha	(1)[7]
0E	1C20A	HTZ (EHZ graphics/HTZ graphics/HTZ placeholders for animated tiles/Fire/Fireballs/HTZ automatic door/GHZ Log bridge/HTZ seesaw/Vertical spikes/Diagonal springs/Vertical spring/Horizontal spring)	(9)
0F	1C254	HTZ (HTZ lift/Buzz Bomber/EHZ Snail/EHZ Piranha)	(0) [4]
10	1C26E	??? (Title card (S1)/)	(0)
11	1C276	Boss (Boss ship/EHZ Boss/EHZ Boss helicopter blades/Boss ship/CPZ Prototype boss/Robotnik's ship boost/Puff of smoke/EHZ Boss/EHZ Boss helicopter blades)	(2)[8]
12	1C2AE	End of level (Signpost/End of level hidden bonuses (S1)/Big ring flash)	(2)
13	1C2C2	??? (INVALID)	(10)
14	1C2C2	??? (INVALID)	(10)
15	1C2C4	GHZ Animals (Bunny/Flicky)	(1)
16	1C2D2	LZ Animals (Penguin/Seal)	(1)
17	1C2E0	CPZ Animals (Squirrel/Seal)	(1)
18	1C2EE	EHZ Animals (Pig/Flicky)	(1)
19	1C2FC	HPZ Animals (Pig/Chicken)	(1)
1A	1C30A	HTZ Animals (Bunny/Chicken)	(1)
1B	1C318	??? (INVALID)	(NA)
1C	1C31A	??? (INVALID)	(NA)
1D	1C31C	??? (INVALID)	(NA)
1E	1C31E	??? (INVALID)	(NA)
1F	1C320	??? (INVALID)	(NA)

Object editing

Object pointers

The object pointers are located at $CB7E. Objects in this list are loaded by referencing their ID (starting from 01). Mainly used by level object layout and debug object lists. Each ID uses 4 bytes, which are 32-bit absolute pointers to the start of programming (ASM code) of a certain object.

ID	Offset	Description	Intended place/Owner/Source
$01	$F9FC	Sonic	Any zone
$02	$10C40	Tails	Any zone
$03	$13E2C	Collision switcher	Any zone
$04	$154D4	Water surface	Water zones
$05	$11D7E	Tails' tails	Tails only
$06	$14970	Spiral path	EHZ
$07	$CDAE	Null object	Anywhere
$08	$12558	Water splash	Sonic
$09	$1A3B8	Sonic	Special Stage
$0A	$11E64	Underwater bubbles	Water zones
$0B	$141B4	Unused alternating platform	CPZ
$0C	$142DC	Unused strange platform	???
$0D	$EF9C	End of level signpost	Any zone
$0E	$B378	Sonic & Tails	Title screen
$0F	$B3FE	???	Title screen?
$10	$1AA5A	???	???
$11	$7BA0	Block bridge	GHZ, HPZ, EHZ
$12	$143DC	Emerald block	HPZ
$13	$14458	Waterfall	HPZ
$14	$14CA0	Seesaw	HTZ
$15	$8204	Swinging platform	GHZ
$16	$15104	Diagonally moving platform	HTZ
$17	$866C	Rotating spike on wooden bridge	GHZ
$18	$880C	Generic natural platform	GHZ, EHZ, HTZ
$19	$152B8	Metal platform	CPZ
$1A	$8C44	Collapsing platform	GHZ, HPZ
$1B	$CDAE	Null object	Anywhere
$1C	$93A4	Bridge support/Moving platform support	GHZ, EHZ, HTZ
$1D	$CDAE	Null object	Anywhere
$1E	$CDAE	Null object	Anywhere
$1F	$A0D0	Crabmeat (badnik)	GHZ
$20	$CDAE	Null object	Anywhere
$21	$1B028	HUD	Any zone
$22	$A408	Buzz Bomber (badnik)	GHZ
$23	$A55E	Buzz Bomber's projectile	Buzz Bomber
$24	$9808	Unknown explosion	???
$25	$A7E4	Ring	Debug
$26	$AE58	Monitor	Any zone
$27	$987C	Dust explosion	Any zone
$28	$9AA8	Animal plus points from badnik explosion	Any zone
$29	$9FA0	Points	Any zone
$2A	$94EC	One way barrier	SBZ
$2B	$B718	Chopper (badnik)	GHZ
$2C	$B7DE	Jaws (badnik)	LZ
$2D	$CDAE	Null object	Anywhere
$2E	$B03A	Monitor contents	Monitor
$2F	$CDAE	Null object	Anywhere
$30	$CDAE	Null object	Anywhere
$31	$CDAE	Null object	Anywhere
$32	$CDAE	Null object	Anywhere
$33	$CDAE	Null object	Anywhere
$34	$B8C8	Title card	Title card
$35	$CDAE	Null object	Anywhere
$36	$C664	Spikes	Any zone
$37	$A91E	Ring spray	Any zone
$38	$123BA	Blue shield	Any zone
$39	$BA84	Game Over/Time Over	Any zone
$3A	$BB46	End of level result screen	Any zone
$3B	$C848	Purple rock	GHZ
$3C	$C8C4	Breakable wall	GHZ
$3D	$18CFC	Robotnik	Any zone
$3E	$194E4	Egg prison	Any zone
$3F	$9914	Fire explosion	Any zone
$40	$F248	Motobug (badnik)	GHZ
$41	$E1C8	Spring	Any zone
$42	$EBB8	Newtron (badnik)	GHZ
$43	$CDAE	Null object	Anywhere
$44	$EEB4	Wall barrier	GHZ
$45	$CDAE	Null object	Anywhere
$46	$CDAE	Null object	Anywhere
$47	$CDAE	Null object	Anywhere
$48	$190E6	Big ball	GHZ boss
$49	$15690	Waterfall	EHZ
$4A	$16AA0	Octus (badnik)	HPZ
$4B	$16794	Buzzer (badnik)	EHZ (HPZ, HTZ)
$4C	$16D50	Batbot (badnik)	HPZ
$4D	$1587C	Tricerabot (badnik)	HPZ
$4E	$171D8	Crocobot (badnik)	HPZ
$4F	$15DA4	Dinobot (badnik)	HPZ
$50	$15F08	"Strange" Aquis (badnik)	HPZ
$51	$16524	Aquis (badnik)	HPZ
$52	$15B4C	Piranha (badnik)	HPZ
$53	$174D0	Masher (badnik)	EHZ
$54	$175D0	Snailbot (badnik)	EHZ (HTZ)
$55	$181CC	???	???
$56	$18456	Unknown double explosion	???
$57	$17884	???	???
$58	$17AEE	???	???
$59	$CDAE	Null object	Anywhere
$5A	$CDAE	Null object	Anywhere
$5B	$CDAE	Null object	Anywhere
$5C	$CDAE	Null object	Anywhere
$5D	$CDAE	Null object	Anywhere
$5E	$CDAE	Null object	Anywhere
$5F	$CDAE	Null object	Anywhere
$60	$CDAE	Null object	Anywhere
$61	$CDAE	Null object	Anywhere
$62	$CDAE	Null object	Anywhere
$63	$CDAE	Null object	Anywhere
$64	$CDAE	Null object	Anywhere
$65	$CDAE	Null object	Anywhere
$66	$CDAE	Null object	Anywhere
$67	$CDAE	Null object	Anywhere
$68	$CDAE	Null object	Anywhere
$69	$CDAE	Null object	Anywhere
$6A	$CDAE	Null object	Anywhere
$6B	$CDAE	Null object	Anywhere
$6C	$CDAE	Null object	Anywhere
$6D	$CDAE	Null object	Anywhere
$6E	$CDAE	Null object	Anywhere
$6F	$CDAE	Null object	Anywhere
$70	$CDAE	Null object	Anywhere
$71	$CDAE	Null object	Anywhere
$72	$CDAE	Null object	Anywhere
$73	$CDAE	Null object	Anywhere
$74	$CDAE	Null object	Anywhere
$75	$CDAE	Null object	Anywhere
$76	$CDAE	Null object	Anywhere
$77	$CDAE	Null object	Anywhere
$78	$CDAE	Null object	Anywhere
$79	$134C8	Lamppost	Any zone
$7A	$CDAE	Null object	Anywhere
$7B	$CDAE	Null object	Anywhere
$7C	$CDAE	Null object	Anywhere
$7D	$13770	Hidden bonus	Any zone
$7E	$CDAE	Null object	Anywhere
$7F	$CDAE	Null object	Anywhere
$80	$CDAE	Null object	Anywhere
$81	$CDAE	Null object	Anywhere
$82	$CDAE	Null object	Anywhere
$83	$CDAE	Null object	Anywhere
$84	$CDAE	Null object	Anywhere
$85	$CDAE	Null object	Anywhere
$86	$CDAE	Null object	Anywhere
$87	$CDAE	Null object	Anywhere
$88	$CDAE	Null object	Anywhere
$89	$CDAE	Null object	Anywhere
$8A	$185E0	Sonic Team Presents/Credits	Title screen/Ending sequence
$8B	$CDAE	Null object	Anywhere
$8C	$CDAE	Null object	Anywhere

Unreferenced objects

The following objects can occupy a valid slot in order to work on their own instead of being summoned by their respective owners:

1. Metal platform's collision mask: $152F0.
2. Aquis' shot (inoffensive): $165AA.
3. Buzzer's shot: $168A0.

The following objects are not summoned by any other object or event and can occupy a valid slot in order to work:

1. Giant ring: $AA72.
2. Flash from giant ring: $AB3C.

Text

Level select text

Level names use non-ASCII characters. See the table below:

00 = 0	01 = 1	02 = 2	03 = 3	04 = 4
05 = 5	06 = 6	07 = 7	08 = 8	09 = 9
0A = $	0B = -	0C = =	0D = <-	0E = <-
0F = Y	10 = Z	11 = A	12 = B	13 = C
14 = D	15 = E	16 = F	17 = G	18 = H
19 = I	1A = J	1B = K	1C = L	1D = M
1E = N	1F = O	20 = P	21 = Q	22 = R
23 = S	24 = T	25 = U	26 = V	27 = W
28 = X		FF = (space)

Miscellaneous

General navigation

Offset	Description
$035A8	Level order information
$02502	Palette pointers
$035A8	Level select level order
$04620	Pointer to collision indexes
$0579A	Level size array
$059C6	Rasterized layer Deformation offset index
$10AF8	Animation script (Sonic)
$1BFEC	Main level load block
$1C05C	Pattern load cues offset index
$1C09C	Pattern load cues
$20000	Curve and resistance mapping (identical to S1)
$20100	Curve and resistance mapping
$20200	Collision Array (identical to S1)
$22200	Collision Array
$28218	Level layout offset index
$40000	Object layout offset index
$50000	Ring location offset index

Level slots

Level ID	Level Name
00	GHZ
01	LZ (loads CPZ art)
02	CPZ (MZ Music)
03	EHZ (SLZ music)
04	HPZ (SYZ music)
05	HTZ (SBZ music)
06	Ending (GHZ art) (crashes)

Main level load block

This is located at $1BFEC, and uses the Sonic 1 format

Level ID	Level Name	8x8 art	16x16 mappings	128x128 mappings	Palette	Song ID	PLRs used
00	GHZ	$D8C34	$D7E34	$DD850	$04	$81	$04, $05
01	LZ	$CC8F4	$CB314	$CFE34	$05	$82	$06, $07
02	CPZ	$CC8F4	$CB314	$CFE34	$06	$83	$08, $09
03	EHZ	$B2184	$B11E4	$B6EB2	$07	$84	$0A, $0B
04	HPZ	$C0492	$BEEB2	$C3314	$08	$85	$0C, $0D
05	HTZ	$B2184	$B11E4	$B6EB2	$09	$86	$0E, $0F
06	Ending	$D8C34	$D7E34	$DD850	$13	$86	None

Debug object lists

These lists are used to tell the game which objects can be placed through debug mode at each zone. They are handled by an offset index at $1BCEC.

List location	Used by
$1BCFA	GHZ
$1BD6C	LZ
$1BD6C	CPZ
$1BDEE	EHZ
$1BF6A	HPZ
$1BED0	HTZ
$1BF6A	Ending

The first two bytes on the list indicate how many objects are there. Each object has 8 bytes: for simply changing which object should appear instead of another, edit bytes 1 & 5, which are object type (ID) and sub-type, respectively.