X-Men.

 No.  Code  Effect
   1  A3YA-AA32  Protection from most enemy hits
   2  BDBA-CA34  Protection from falling off screen (no health lost)
   3  ACJT-CAGA  Protection from spikes
   4  AB1A-CAGJ + AB1T-CAHE  Gambit's lethal burst uses no mutant power
   5  DKWA-CA4C + DVWA-CA6L    Nightcrawler's teleport uses no mutant power
   6  ALKT-CA4L  Wolverine's claws use no mutant power
   7  ABET-CAAE + ABDT-CAG8  Wolverine's spin slash uses no extra mutant power
   8  ABMT-CAE2 + ABNA-CAFA  Cyclops' eye-beam uses no mutant power
 - except when you duck or jump
   9  ABPA-CAC6 + ABMA-CAC4  Cyclops' optic blast uses no mutant power
 10  ACKT-CAFT  Mutant power does not regenerate
 11  TCKT-CAFT  Mutant power regenerates faster
 12  ACKT-CEFT  Mutant power regenerates much faster
 13  ACKT-CJFT  Mutant power regenerates to full very quickly
 14  BC7A-CA5W  Lets you use Iceman multiple times
 15  BC9T-CA80  Lets you use Archangel multiple times
 16  BC8T-CA42  Lets you use Rogue multiple times
 17  BC7T-CA2T  Lets you use Storm multiple times
 18  P0KT-DAYW  Wolverine heals himself faster
 19  ALKA-CA86  Switch X-Men an infinite number of times
 20  AP6T-EAF2  Start part way through Savage Land
 21  AV6T-EAF2  Start in Shi'ar Empire
 22  AZ6T-EAF2  Start on Excalibur's Lighthouse stage
 23  A36T-EAF2  Start inside Excalibur's Lighthouse
 24  A76T-EAF2  Start in Ahab's Future World
 25  BB6T-EAF2  Start in Mojo's Crunch
 26  BK6T-EAF2  Start in Asteroid M
 27  B5BA-CA7T  No mutant power lost when Wolverine falls off screen