Sonic 2 Hacking Guide
Genecyst Savestate - Basic Configurations

You can configure the basics of memory with these notes. 'Basics' refers to things such as current level, lives, continues, score, rings, etc. This offers you a large range of ways to cheat as well.

011BD8 (F760) - Max speed (16-bit)
011BDA (F762) - Acceleration (16-bit)
011BDC (F764) - Slow down (16-bit)
012288 (FE10) - Level
012289 (FE11) - Act
01228A (FE12) - Lives for player 1
012290 (FE18) - Continues
012298 (FE20) - Rings for player 1 (16-bit)
01229B (FE23) - Minutes on clock for player 1
01229C (FE24) - Seconds on clock for player 1
01229D (FE25) - Middle seconds on clock for player 1
01229E (FE26) - Score for player 1 (32-bit)
0122AA (FE32) - Star post check X position for player 1 (16-bit)
0122AC (FE34) - Star post check Y position for player 1 (16-bit)
01233E (FEC6) - Lives for player 2
012348 (FED0) - Rings for player 2 (16-bit)
01234B (FED3) - Minutes on clock for player 2
01234C (FED4) - Seconds on clock for player 2
01234D (FED5) - Middle seconds on clock for player 2
01234E (FED6) - Score for player 2 (32-bit)
01235A (FEE2) - Star post check X position for player 2 (16-bit)
01235C (FEE4) - Star post check Y position for player 2 (16-bit)
0123E9 (FF71) - Player in special stage [Yarharhar]
0123EB (FF73) - Player in game [Yarharhar]
0123ED (FF75) - Teleport only in 2 player mode
012429 (FFB1) - Emeralds