Sonic the Hedgehog PAR

[ian]

Keep XX rings
00D2 AAXX

Unlimited lives
00D2 4603

Turbo Sonic
00D4 1105

Funky Graphics
00D2 A5XX - Speed of Graphic change (01 being fastest, I recommend FF)
00D2 A7FF
00D2 A8FF
00D2 A9FF

Level select
00D2 3EXX
Replace XX with one of the following values. Enable the code before the game starts, then disable after the level begins.
00: Green Hill 1
01: Green Hill 2
02: Green Hill 3
03: Bridge 1
04: Bridge 2
05: Bridge 3
06: Jungle 1
07: Jungle 2
08: Jungle 3
09: Labyrinth 1
0A: Labyrinth 2
0B: Labyrinth 3
0C: Scrap Brain 1
0D: Scrap Brain 2
0E: Scrap Brain 3
0F: Sky Base 1
10: Sky Base 2
11: Sky Base 3
12: End Game

[Melanogaster]

00D2 CEYX
Keep the timer at X minutes (replace the YX on the code for a number between 00 and 09. Entering 09 will lead you to death after the first minute (due to the 9:59 -► 10:00 internal changing on the timer), unless you use the following PAR code to lock the seconds)

00D2 CFXX
Keep the timer at XX seconds (replace the XX on the code for a number from 00 to 59. Entering 59 will actually advance one minute every second, so it shouldn't be entered if: (a) the previous PAR code is set to show 9:00 (or else you'll die within one second), or (b) the previous PAR code is not used simultaneously with this code (or else you'll die within ten seconds)

[ian]

Infinite Air
00D2 9C00

Special Bonus
For a long time I've wondered how the Special Bonus you get when completing the game is calculated. Now I've finally cracked it!

It's the sum of these achievements:

Collecting all 6 emeralds - 50,000 points
Collecting all 12 lives (one on every level) - 50,000 points
Playing all 8 bonus stages - 50,000 points
Completing all 8 bonus stages - 50,000 points
Not losing a life - 100,000 points

If you manage to achieve all of those things, you'll get a 200,000 bonus, coming to a massive 500,000 points overall.

[Melanogaster]

Ahh, nice find... I've always wondered if I could get past the 500,000 mark; guess that's indeed not possible, then.