Easy Lives:

In level 1, area 1, there is a breakable wall under the G square (get the G then jump down to the lighter patch, revealing a barrel) press and
hold B to pick up the barrel. walk to the left until u fall off the raised part then walk back to the left, breaking the wall. match 3 barrels
with the same animal to receive the trophy. u will return to the game where u picked up the barrel. move to the left then walk through the already broken wall and repeay until 99 lives is reached.  (recive 3 matching trophies [does not have to be in a row] to receive bonus. get 100 small trothies to receive extra life. after bonus will be returned to check point).
Sent in by: alksdf

Fifty lives - Hold Select and press B, A, R(2), A, L at the game selection screen. A sound will confirm correct code entry. When you start the game, you will now have 50 lives.

In-game reset - Press Start to pause game play, then press Select to exit the current level. Note: This can only be done in levels that have been previously completed.

Hero mode - Successfully complete the game with a 100% rank. Start a new game and select two player mode to access the "Hero mode" option. In this mode, you play as Diddy Kong only, with a new costume. There are no Donkey Kong Barrels, Checkpoint Barrels, and pictures.

Get Diddy's or Donkey Kong's boat to move when fishing - When fishing, get a combo. When you see the exclamation mark above Diddy's head, you can go somewhere and he will follow you. - This will help you catch more fish and get more combos.

Exit Previously Beaten Levels - Once you've beaten a level you can press Start and then Select in the level to exit it.

Start/Continue a file with 50 lives - At the file select screen, go down to the erase command at the bottom of the screen. Hold select, and input the following buttons: B-A-R-R-A-L-L.

Diddy will then say ''Not Bad''. Now, load any of the three game files, and you will automatically start with 50 lives. You do not have to input this code again as long as you save.
Sent in by NillKaboo

Bonus Stage

Code Effect  -  At the main menu press Start, then hold Select and press B, Up, B, B, A Bonus Stage

Get the Sound Test menu  -  To see the sound test menu and listen to music from the game, at the start screen, hold select button, then press B,A,L,L,A, Down. Now, youll see the Sound player.

Code Effect  -  B, A, L, L, A, Down Unlock the Sound Test menu

Start/Continue a file with 50 lives  -  At the file select screen, go down to the erase command at the bottom of the screen. Hold select, and input the following buttons. Diddy will say ''Not Bad''. Now, load any of the three game files, and you will automatically start with 50 lives. You do not have to input this code again as long as you save.

Code Effect  -  B-A-R-R-A-L Start/Continue a file with 50 lives

Unlockables  -  Alternate DK Attack Background

How to Unlock  -  Alternate backgrounds for DK attack level select screen Get an S rank on all of the DK attack levels.

Unlimited Time Bonus on Bouncy Bonanza  -  Right after the part where you get the frog, drop down to the ledge on the right. You will be back in the same room and you can collect the +5 multiplier again. Rinse and Repeat for as big of a time bonus as you want!

Cheat Device Codes:

1E Enable Code (Must Be On) 0000DB78 000A  10000B8C 0007
Transparent [Note 1] 3300133C 0002
Always Have Partner 73000FD6 0000  33000FD6 0001
Infinite Lives 33000FC8 0009 
4 Have K.O.N.G Letters 43000F34 0002  00000004 0004
1 Winky = 3 33001007 0002
1 Rambi = 3 33001004 0002
1 Expresso = 3 33001005 0002
1 Enguarde = 3 33001006 0002
Scrap Book Complete 43001176 FFFF  00000004 0002  3300117E 00FF
Access Funky 33001187 0001
Access All Areas 83001040 FFFF
Access All Stages 43001036 FFFF  00000005 0002
All Stage Bonus's Found 33001008 00F0  3300101D 00FF  4300101E FFFF  00000004 0002
DK's Attack Complete Codes [Note 2]
1st Save Slot 72000D3A FFFF  42000D4A FFFF  00000006 0002
2nd Save Slot 72000D9A FFFF  42000DAA FFFF  00000006 0002
Access Bonus Level Codes [Note 3]
Press R+B+Up For Rambi 74000130 02BD  32000D38 0008  74000130 02BD  32000D40 0004  74000130 02BD  33000F28 0028
Press R+B+Right For Expresso 74000130 02ED  32000D38 0008  74000130 02ED  32000D40 0004  74000130 02ED  33000F28 0029
Press R+B+Down For Enguarde 74000130 027D  32000D38 0008  74000130 027D  32000D40 0004  74000130 027D  33000F28 002A
Press R+B+Left For Winky 74000130 02DD  32000D38 0008  74000130 02DD  32000D40 0004  74000130 02DD  33000F28 002B
<>
(m)  b9061533  a0f44341  d18b2a92  33d7c96f
All Scrapbook  b0c97063  2b55dbf9  26834b64  4f498ed5
Invincible  6d957522  fa7f51e4
Infinite Lives  aa3cf642  999874d