Sonic & Knuckles.
 No.  Code  Effect
   1  AFKT-AAG0  Start with 1 life instead of 3
   2  AKKT-AAG0  Start with 2 lives
   3  AVKT-AAG0  Start with 4 lives
   4  AZKT-AAG0  Start with 5 lives
   5  A7KT-AAG0  Start with 7 lives
   6  BFKT-AAG0  Start with 9 lives
   7  DFKT-AAG0  Start with 25 lives
   8  GKKT-AAG0  Start with 50 lives
   9  NPKT-AAG0  Start with 99 lives
 10  K2WA-CA4J  Infinite lives
 11  AWXT-CA4C  Don't lose rings when hit
 12  HXRT-AA6A  Infinite time
 13  96BA-CAG6 + 98MA-CAF0  Keep shields (fire, water, lightning) when hit
 14  AKVT-AA76 + AMNA-EA24  Keep rings between levels
 15  ATGT-CA3Y  Super shoes don't run out with time
 16  RENT-C6YA  Sonic can always double jump
 (can't use water shield or become Super Sonic)
 17  RENT-C6V6  Sonic can always use Fireball Spin Dash
 (can't double jump, bounce, or become Super Sonic)
 18  RGSA-A6YY  Only 1 blue sphere needed to get a chaos emerald
 19  AANA-CNA0  Sonic jumps as high as Knuckles (slightly lower than usual)
 20  4ANA-CRA0  High jump for Sonic
 21  2ANA-CWA0  Super jump for Sonic
 22  AANA-C4A0  Mega jump for Sonic
 23  AANA-DYA0  Orbital jump for Sonic
 24  TB5T-CNCR  Knuckles jumps as high as Sonic (slightly higher than usual)
 25  PV5T-CRCR  High jump for Knuckles
 26  AB5T-CWCR  Super jump for Knuckles
 27  AB5T-C2CR  Mega jump for Knuckles
 28  AB5T-DTCR  Orbital jump for Knuckles
 29  ALNA-AACR  Rings worth 2 in special stage
 30  ARNA-AACR  Rings worth 3 in special stage
 31  AWNA-AACR  Rings worth 4 in special stage
 32  A0NA-AACR  Rings worth 5 in special stage
 33  BLNA-AACR  Rings worth 10 in special stage
 34  A2NT-CAG6  Only 6 chaos emeralds needed to become Super Sonic
 35  AYNT-CAG6  Only 5 chaos emeralds needed to become Super Sonic
 36  ATNT-CAG6  Only 4 chaos emeralds needed to become Super Sonic
 37  ANNT-CAG6  Only 3 chaos emeralds needed to become Super Sonic
 38  AJNT-CAG6  Only 2 chaos emeralds needed to become Super Sonic
 39  AENT-CAG6  Only 1 chaos emerald needed to become Super Sonic
 40  AANT-CAG6  Become Super Sonic without any chaos emeralds
 41  NTNT-CAHL  100 rings needed to become Super Sonic instead of 50
 42  FANT-CAHL  40 rings needed to become Super Sonic
 43  DENT-CAHL  25 rings needed to become Super Sonic
 44  BJNT-CAHL  10 rings needed to become Super Sonic
 45  AENT-CAHL  1 ring needed to become Super Sonic
 46  AANT-CAGY+AAPA-CAB8  Become Super-Duper Sonic without any emeralds
 (you still need 50 rings unless using one of the above codes)
 47  NTPT-CA50  Rings aren't used as Super (or Super-Duper) Sonic/Knuckles
 48  RHJA-E60L  Bonus round always activated after every checkpoint
 49  BXLA-EA5G  Bonus round is always Slot Machine
 50  A5LA-EA5G  Bonus round is always Glowing Spheres
 51  A36A-CACW  Only 6 chaos emeralds needed to become Super Knuckles
 52  AZ6A-CACW  Only 5 chaos emeralds needed to become Super Knuckles
 53  AV6A-CACW  Only 4 chaos emeralds needed to become Super Knuckles
 54  AP6A-CACW  Only 3 chaos emeralds needed to become Super Knuckles
 55  AK6A-CACW  Only 2 chaos emeralds needed to become Super Knuckles
 56  AF6A-CACW  Only 1 chaos emerald needed to become Super Knuckles
 57  AB6A-CACW  Become Super Knuckles without any chaos emeralds
 58  NV6A-CADA  100 rings needed to become Super Knuckles instead of 50
 59  FB6A-CADA  40 rings needed to become Super Knuckles
 60  DF6A-CADA  25 rings needed to become Super Knuckles
 61  BK6A-CADA  10 rings needed to become Super Knuckles
 62  AF6A-CADA  1 ring needed to become Super Knuckles
 63  AB6A-CACL + AB6A-CAHR  Become Super-Duper Knuckles without any emeralds
 (you still need 50 rings unless using one of the above codes)
 64  ACCT-CA2R  Can't drown