Just like a backstage pass for monkeys, this grants access to all levels in the game, even the secret levels. As an added bonus, this also gets you the Bloons 2 Level Editor.
~ Upgrade description

The Unlock All Levels upgrade is available in the Bloons 2 game in the Bloons 2 Store for 3,000 MochiCoins. It unlocks all levels in Bloons 2, including all the secret ones, as well as access to the Bloons 2 Level Editor.