Sonic the Hedgehog
1 ATBT-AA32 MASTER CODE--MUST BE ENTERED
SOME CODES DON'T WORK WHEN YOU START ON SPECIAL STAGES USING CODE 13
4 AE0T-CABE Once invincible, stay invincible for the rest of stage or until you die
11 SCRA-BAX0 Each ring counts as 8
12 GJ6A-CA7A Infinite lives
13 AJ3A-AA4G Level select menu (hold A and press start while sonic waves finger in start screen)
14 AY3T-BA4R Start with 5 chaos emeralds
15 DDLT-AAGL Super jump
16 BDLT-AAGL Skywalking
18 AEOT-CABY Once you have shoes, keep shoes for the rest of stage or until you die

Sonic the Hedgehog 2
7A SAST-DA1A Rings worth 8--player 1
7B SATA-DATJ
16A JW3A-CA4J Infinite lives--player 1
16B JW3A-CA4Y
FOR CODES 35 AND 36, SWITCH OFF IF YOU GET STUCK SOMEWHERE OR WANT TO SINK IN WATER
36A CBVT-CAE2 Jump really high
36B CBVT-CAE2
40A ALTA-CA9J Once invincible (stars), Sonic stays Invincible for the rest of the level
40B ALTA-CA9Y
41A ATTT-CA4W Sonic doesn't lose rings when hit
41B ATTT-CA58
42A ATTT-CA5G Tails doesn't lose rings when hit
42B ATTT-CA6W
43A AH2T-CAH6 Sonic needs only 1 ring instead of 50 to enter special stage after touching a star post
43B AH2T-CAHN
WITH CODES 44 THRU 57, THE COUNTER DOESN'T SHOW THE EXTRA RINGS, BUT YOU DO GET THEM
50A SBJA-HAWJ Rings worth 8 in special stages--Sonic
50B SBJA-HAV2
57A SBJA-HAWR Rings worth 8 in special stages--Tails
57B SBJA-HAV8
FOR CODES 58 THRU 64, DON'T GRAB MORE CHAOS EMERALDS THAN THE AMOUNT YOU NEED
58A ACZT-CACA Need 0 chaos emeralds to become Super Sonic (in addition to rings)
58B ACZT-CACN
63A A0ZT-CACA Need 5 chaos emeralds to become Super Sonic (in addition to rings)
63B A0ZT-CACN
64A A4ZT-CACA Need 6 chaos emeralds to become Super Sonic (in addition to rings)
64B A4ZT-CACN
65A AGZT-CACJ + K4ZT-CA9N Need 1 ring to become Super Sonic (in addition to chaos emeralds), don't lose rings with time
65B AGZT-CACY+ K4ZT-CA92
71A RE8A-A60W Level select menu--at title screen, hold down A while pressing start
71B RE8A-A60G
72A 2VAT-BCRN Start most levels with some rings--1-player game only (number of rings varies with stage, and you can still lose rings)
72B 2VAT-BCRA

Sonic the Hedgehog 3
1 AWHA-CA92 Don't lose rings
8 SCGT-DAYL Rings worth 8
29 AJZA-CA8N Super Sonic doesn't lose rings
30 AJ3A-CA7A Infinite lives
38 ACAT-CAB6 Shield can be activated multiple times
39 AJRT-CA8R Invincibility power-ups last forever
46 SCFT-B2T4 Only need 2 chaos emeralds
54 ACGA-AA8T 1 Blue sphere needed for chaos emerald
57 AAYA-C0B6 Mega-jump
58 ATST-CA38 Never drown (must switch off for some spring-pad jumps)

Sonic and Knuckles
CODES 1 THRU 10 ARE ONLY FOR THE SONIC & KNUCKLES GAME ALONE
10 K2WA-CA4J Infinite lives
CODES 11 THRU 64 WORK FOR SONIC & KNUCKLES GAME ALONE AND ALSO WITH SONIC 3 GAME ATTACHED
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
18 RGSA-A6YY Only 1 blue sphere needed to get a chaos emerald
23 AANA-DYA0 Orbital jump for Sonic
28 AB5T-DTCR Orbital jump for Knuckles
33 BLNA-AACR Rings worth 10 in special stage
40 AANT-CAG6 Become Super Sonic without any chaos emeralds
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 up as Super (or Super-Duper) Sonic/Knuckles
57 AB6A-CACW Become Super Knuckles without any chaos emeralds
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
CODES 65 THRU 86 ARE FOR KNUCKLES IN THE SONIC 2 GAME
65 AX6D-AA3W Knuckles doesn't lose rings when hit
66 HWLX-GA2Y Infinite time
73 SD5X-BAT2 Rings worth 8
82 JV1D-CA6W Infinite lives
86 ABWD-DTDC Orbital jump for Knuckles