Bugs:Sonic the Hedgehog 2 (Genesis)
This page details bugs of Sonic the Hedgehog 2 (Genesis).
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Sonic 2 has many bugs, some of which were fixed in later revisions of the game.
Gameplay Bugs
Multiple Points for Separate Players in 2-Player Mode
If Sonic/Tails destroys a badnik, and Tails/Sonic quickly destroys another badnik in 2-player mode, Sonic/Tails will get 200 points, and vice-versa.
Super Sonic at End of Level
There's an extremely horrible bug that can occur as Super Sonic. If the player has at least 50 rings and transforms at the end of the level before going off-screen, Sonic will turn to normal but will be stuck in the air, basically softlocking the game. This was thankfully fixed in REV02.
A similar bug can occur with capsules, though because the results display no matter what, this will not softlock the game.
Over 999 Rings
In REV00 only, it's possible for ring monitors to exceed the 999-ring cap, which will glitch out the HUD. Fixed in REV01.
This was fixed in the Sonic Mega Collection version, which is based on REV01.
Debug Mode Crash
Placing an object in Debug Mode after dying will crash the game due to a word operation at an odd address.
61 Frame Draining
Due to a programming oversight, the Super Sonic ring drain is actually 61 frames instead of 60. This essentially gives the player an extra second per 60 rings.
Missing Super Sonic Palette Frame
When the game does the palette cycle routine for Super Sonic, it uses "blo" instead of "bls". As a result, it skips the last frame of animation.
Tails' Underwater Rolling Deceleration
Funnily, Tails' rolling code is the same as Sonic's in Sonic 1, which means Tails decelerates much slower underwater than Sonic.
Graphical Bugs
Missing Arm
On the title screen, Sonic's arm disappears for one frame.
Boss Deconstruction
The Aquatic Ruin, Casino Night, and Mystic Cave boss addons don't fall apart as they should. For all other bosses the parts fall in individual directions, but here they either fall in the same direction (Aquatic Ruin) or the wrong one (Casino Night/Mystic Cave).
Level-Specific Bugs
Broken Title Card Frame
One of the frames of Emerald Hill Zone's title card doesn't display properly. Oddly, this only became an issue in Beta 5.
Broken Horizontal Scrolling in Emerald Hill Zone
In Emerald Hill Zone, the bottom two pixels don't scroll correctly. This was fixed in Knuckles in Sonic 2 and 3D Sonic the Hedgehog 2, but not in the vanilla version of the game.
Tails Acts Strangely in Casino Night
In Casino Night Zone, Tails sometimes uses his standing animation when moving.
Rexon Crash
If the player breaks a rock and then destroys a Rexon in a certain way, the game will crash. This is because the game is jumping to code it's never meant to, resulting in invalid opcodes and an eventual crash.
This was fixed in REV02.
Can't Spindash Off Tornado
In the Sonic Classics version of REV02, it's not possible to spindash off the Tornado.
While one could argue that being able to spindash off the Tornado is a bug in itself, it does seem intentional as it happens in every other version of the game including the 2013 remake.
Sound Driver Bugs
14 Continues Cheat
Using the 14 continues cheat (01, 01, 02, 04) will continuously play the Oil Ocean Zone theme. This is because instead of playing $BF (the continue sound), it instead plays $3F. As that is an invalid SMPS command, it causes the Sound Driver to malfunction and be unable to play new sounds.
Death Egg Music Doesn't Resume
The game is programmed to restart the Death Egg theme after beating Mecha Sonic...in theory. However, the instruction uses the wrong data length to pass Death Egg's music identifier to the function for switching tracks, resulting in the game instead pointlessly trying to play track #0.
Higher-Pitch Sega Sound
The "Seega!" chant at the beginning at the game is slightly higher pitched than it should be (this is noticeable when compared to Sonic 1/3K).
