Cheat Crash Bandicoot XS (E) GBA :

After getting 100% (all gems + at least all gold relics), if you go back
and defeat the final boss a second time, you will unlock an extra level
with the ''monster'' (mutated bosses) chasing you. Making it to the end
of this extra level will get you 101%.

- Codebreaker

Enable Code (Must Be On) 
00008F0E 000A
100007AC 0007

Infinite Lives 
32000098 0063

Infinite Mask 
8200009C 0003

Infinite Health (Flying Stages) 
83003F44 0064

Have Special Moves 
32000026 00F0

Start With 100 Boxes 
72000094 0000
82000094 0064

Timer Off 
820000BC 0000

Press A For Moon Jump 
D0000020 0001
32010A78 00CC

Extra level
-----------
When you get 100% complete.

Enable Code (Must Be On)
93C33422 4F7A
42D64A0A FC29
3FE3B7B9 A55E

Infinite Lives
BD105EB9 2A77

Infinite Mask
EF7757D9 BCFA