These codes are for the newest version of Yoshi's Island DS. To see which version you have, put your game in the Action Replay unit and match the Game ID that shows up at the bottom of "Unknown Game".
Game ID: AYWE-52E1DC28
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Source: Codejunkies

Infinite Lives
220ecd10 00000063

Infinite Mario Time (30 Stars)
b20ed1d0 00000000
10000008 0000001e
d2000000 00000000

EGG CODES:

Swallow 1 Enemy for 7 Eggs
920edc84 00000001
220edc84 00000007
d2000000 00000000

Press R to Fill Eggs
94000130 feff0000
220edc84 00000007
d2000000 00000000

All Character Coins Found (All Worlds)
220ece3f 000000ff
020ece40 ffffffff
220ece44 000000ff

Museum Complete
020eceb0 ffffffff
020eceb4 ffffffff
020eceb8 ffffffff

ALL STAGES COMPLETE CODES:
Do not use with any STAGES COMPLETE PERFECT / NO SCORE CODES!

All Stages Complete (No Score)
d5000000 00000101
c0000000 00000018
d7000000 020ecd14
d2000000 00000000

All Stages Complete (Perfect Score)
d5000000 00006565
c0000000 00000018
d7000000 020ecd14
d2000000 00000000

STAGES COMPLETE WITH NO SCORE CODES:
Do not use with ALL STAGES COMPLETE or PERFECT SCORE CODES!

World 1-1 No Score
220ecd14 00000001

World 1-2 No Score
220ecd15 00000001

World 1-3 No Score
220ecd16 00000001

World 1-4 No Score
220ecd17 00000001

World 1-5 No Score
220ecd18 00000001

World 1-6 No Score
220ecd19 00000001

World 1-7 No Score
220ecd1a 00000001

World 1-8 No Score
220ecd1b 00000001

World 1-Secret No Score
220ecd1c 00000001

World 1-Extra No Score
220ecd1d 00000001

World 2-1 No Score
220ecd1e 00000001

World 2-2 No Score
220ecd1f 00000001

World 2-3 No Score
220ecd20 00000001

World 2-4 No Score
220ecd21 00000001

World 2-5 No Score
220ecd22 00000001

World 2-6 No Score
220ecd23 00000001

World 2-7 No Score
220ecd24 00000001

World 2-8 No Score
220ecd25 00000001

World 2-Secret No Score
220ecd26 00000001

World 2-Extra No Score
220ecd27 00000001

World 3-1 No Score
220ecd28 00000001

World 3-2 No Score
220ecd29 00000001

World 3-3 No Score
220ecd2a 00000001

World 3-4 No Score
220ecd2b 00000001

World 3-5 No Score
220ecd2c 00000001

World 3-6 No Score
220ecd2d 00000001

World 3-7 No Score
220ecd2e 00000001

World 3-8 No Score
220ecd2f 00000001

World 3-Secret No Score
220ecd30 00000001

World 3-Extra No Score
220ecd31 00000001

World 4-1 No Score
220ecd32 00000001

World 4-2 No Score
220ecd33 00000001

World 4-3 No Score
220ecd34 00000001

World 4-4 No Score
220ecd35 00000001

World 4-5 No Score
220ecd36 00000001

World 4-6 No Score
220ecd37 00000001

World 4-7 No Score
220ecd38 00000001

World 4-8 No Score
220ecd39 00000001

World 4-Secret No Score
220ecd3a 00000001

World 4-Extra No Score
220ecd3b 00000001

World 5-1 No Score
220ecd3c 00000001

World 5-2 No Score
220ecd3d 00000001

World 5-3 No Score
220ecd3e 00000001

World 5-4 No Score
220ecd3f 00000001

World 5-5 No Score
220ecd40 00000001

World 5-6 No Score
220ecd41 00000001

World 5-7 No Score
220ecd42 00000001

World 5-8 No Score
220ecd43 00000001

World 5-Secret No Score
220ecd44 00000001

World 5-Extra No Score
220ecd45 00000001

STAGES COMPLETE WITH PERFECT SCORE CODES:
Do not use with ALL STAGES COMPLETE or NO SCORE CODES!

World 1-1 Perfect Score
220ecd14 00000065

World 1-2 Perfect Score
220ecd15 00000065

World 1-3 Perfect Score
220ecd16 00000065

World 1-4 Perfect Score
220ecd17 00000065

World 1-5 Perfect Score
220ecd18 00000065

World 1-6 Perfect Score
220ecd19 00000065

World 1-7 Perfect Score
220ecd1a 00000065

World 1-8 Perfect Score
220ecd1b 00000065

World 1-Secret Perfect Score
220ecd1c 00000065

World 1-Extra Perfect Score
220ecd1d 00000065

World 2-1 Perfect Score
220ecd1e 00000065

World 2-2 Perfect Score
220ecd1f 00000065

World 2-3 Perfect Score
220ecd20 00000065

World 2-4 Perfect Score
220ecd21 00000065

World 2-5 Perfect Score
220ecd22 00000065

World 2-6 Perfect Score
220ecd23 00000065

World 2-7 Perfect Score
220ecd24 00000065

World 2-8 Perfect Score
220ecd25 00000065

World 2-Secret Perfect Score
220ecd26 00000065

World 2-Extra Perfect Score
220ecd27 00000065

World 3-1 Perfect Score
220ecd28 00000065

World 3-2 Perfect Score
220ecd29 00000065

World 3-3 Perfect Score
220ecd2a 00000065

World 3-4 Perfect Score
220ecd2b 00000065

World 3-5 Perfect Score
220ecd2c 00000065

World 3-6 Perfect Score
220ecd2d 00000065

World 3-7 Perfect Score
220ecd2e 00000065

World 3-8 Perfect Score
220ecd2f 00000065

World 3-Secret Perfect Score
220ecd30 00000065

World 3-Extra Perfect Score
220ecd31 00000065

World 4-1 Perfect Score
220ecd32 00000065

World 4-2 Perfect Score
220ecd33 00000065

World 4-3 Perfect Score
220ecd34 00000065

World 4-4 Perfect Score
220ecd35 00000065

World 4-5 Perfect Score
220ecd36 00000065

World 4-6 Perfect Score
220ecd37 00000065

World 4-7 Perfect Score
220ecd38 00000065

World 4-8 Perfect Score
220ecd39 00000065