To unlock the Spot The Sneak mini-game, play all four player mini-games in Free Play mode.

Unlock the following  difficulty levels by performing the corresponding tasks:

DIFFICULTY LEVEL - HOW TO UNLOCK
Expert CPU player difficulty - Defeat CPU players set to Advanced difficulty in a Party mode.
Master CPU player difficulty - Defeat CPU players set to Expert difficulty in a Party mode.

Unlock the following mini-games in Challenge mode by performing the corresponding tasks:

MINI-GAME - HOW TO UNLOCK
Banana Blockade (two player) - Play its normal version in any mode.
Clover Hunt (single player) - Play its normal version in any mode.
Shifty Gifts (single player) - Play its normal version in any mode.
Tippy Traverse(two player) - Play its normal version in any mode.

Unlock the following difficulty levels by performing the corresponding tasks:

DIFFICULTY LEVEL - HOW TO UNLOCK
Balance Boat Time Attack Beginner - Successfully complete Balance Boat under the Expert difficulty setting.
Balance Boat Time Attack Intermediate - Successfully complete Balance Boat Time Attack Beginner.
Balance Boat Time Attack Expert - Successfully complete Balance Boat Time Attack Intermediate.