It's known for being the first compilation of Sonic games, and the last Sonic game released for the Sega Genesis prior to leaving the North American market (Although Sonic 3D Blast was the last "new" Sonic game released in PAL regions, and the promotional Sonic 3 movie cartridge is the last Sonic game released officially for the Sega Genesis).
In Dr. Robotnik's Mean Bean Machine, the code to prevent the Sound Test from being displayed has been modified. The code to check the Hardware Version is still there, but the rest of the instructions have been set to no operation (with two instructions not doing anything useful). Then 0000 is moved to the RAM at 00FFFC02 (so the Sound Test will not display).
Code is activated before the SEGA Logo (Sonic Classic - USA/Europe V1.1):
1224F6 10 39 MOVE.B ($00A10001),D0 ; Copy Hardware Version Byte (A10001) to D0.
1224FC 02 00 ANDI.B #$C0,D0 ; Perform a logical AND on C0 and byte in D0 (basically
bits 5 to 0 will always become 0, while bit 7 [Region]
and bit 6 [Display] are kept the same).
122500 04 00 SUBI.B #$00,D0 ; Subtract 0 from D0.
122504 4E 71 NOP ; No operation.
122506 4E 71 NOP ; No operation.
122508 4E 71 NOP ; No operation.
12250A 4E 71 NOP ; No operation.
12250C 13 FC MOVE.B #$00,($00FF0A3A) ; Move 00 to FF0A3A.
122514 4E 75 RTS ; Return to start.
Code is activated before the Title Screen (Sonic Classic - USA/Europe V1.1):
10E10C 33 FC MOVE.W #$0000,($00FFFC02) ; Move 0000 to FFFC02.
10E114 61 00 BSR #$0BAE [10ECC4] ; Jump to 0BAE.
For unknown reasons (possibly due to poor compression), this compilation's versions of Sonic 1 and Sonic 2 introduces several bugs which weren't in the original games:
This page or section needs more images. There's a whole lotta words here, but not enough pictures. Please fix this. Specifically: Get a visual comparison between the regular cycling palette and the corrupted one.
Due to the different ROM addresses, it introduces a bug where Scrap Brain's palette cycling is bugged. This is due to the pointers for the palette data coming after 0x10000, while the original game's pointers being 0xFFFF. As a result, the game pulls the new palette entries from junk data.
In version 1.0, the "All Chaos Emeralds" code (04, 01, 02, 06 in the Level Select) will not play the Emerald sound effect. Version 1.1 fixes this.
Grabber
Mecha Sonic
Grabber's legs and Mecha Sonic's flame and sparks aren't properly flipped if they're facing right.
Please elaborate. Having more detail is always a good thing. Specifically: It's unclear what the following bullet point means, it should probably be reworded.
The player cannot Spin Dash off the Tornado in Sky Chase Zone. This is since the original game checking for whether the player was standing on the Tornado, while this compilation checks if they're only facing left.
The vertical conveyor belt platforms in Wing Fortress Zone do not make the player fall when they retract into the wall, causing the player to stand on air.
If you touch a launcher or go on a platform or get hurt, you get back to normal.
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