Once you collect all the collectibles you can access the level where you can use these codes.

1.
Turns you into the dog from the hub.

2.

Makes kiwi huge.

3.

Turns you into the enemy.

4.

Low gravity.

5.

Turns you into the embryo looking thing.

6.

Unlocks a secret level from the original Kiwi 64 and gives you the 50th collectible

7.

Turns you into a collectible?? For some reason.

8.

First person mode (lmao).