A Boy and His Blob is separated into four worlds, each with a Hideout, ten Regular Stages, ten Challenge Stages, and a Boss at the end. Each world revolves around a different setting.
The object in each stage is to reach the Golden Jelly Bean at the end. When you reach it, the Blob will eat it and turn into a door leading back to your Hideout. After the tenth stage of a world, you will face a Boss. Defeat the Boss to unlock the next world.
Remember that the Boy is just that—a boy. He cannot jump very high, and he will die if he is exposed to any hazard (Black Blobs, spikes, water, bottomless pits, falls from too high, etc.). However, the game does not count lives, so you cannot "lose" the game: only be blocked. Should you feel stumped or simply don't wish to continue, you can pause the game at any time and choose to return to your Hideout.
The game features an automatic saving feature. The first time you run the game, a profile is created for you. This profile will automatically be updated each time you clear a stage or reach some other milestone. To avoid losing your profile, do not turn off or otherwise interrupt the Wii while a loading screen (a black screen with an animation in the center) is present.
You can choose to erase the progress of your profile by using the Trashcan in each of your Hideouts.
Each world has a Hideout from which the Boy will select stages and collect treasures from the varying stages. Collecting all three Treasure Chests from a Regular Stage will add an item to the Challenge Room; this represents a Challenge Stage you can attempt. Once you complete the Challenge Stage, another item will be added somewhere in the Hideout. Each represents Behind The Scenes material about the game's production.
You can revisit any stage you've previously cleared (such as to try to collect the Treasure Chests), and once you unlock a second Hideout, you can quickly switch between Hideout to jump between worlds.
Should you leave the game and return, you will automatically restart from the last Hideout you reached.
Each of the normal stages challenges you to reach the end by avoiding obstacles and employing the powers available to the Blob by use of your Jelly Beans. Most of these stages have checkpoints where you will restart should you die.
Also within each Regular Stage are three Treasure Chests. If you lead the Blob to one, he will eat it. You can use the Bean Menu to track your Treasure Chest progress. Completing the stage unlocks the next stage (or the Boss if it is the tenth stage). Doing to while collecting all three of the Treasure Chests unlocks a Challenge Stage. Note that Treasure Chests are only recorded and saved by completing the stage. Returning to Base abandons progress for that stage.
The Challenge Stages are self-explanatory. They are more difficult stages with no Treasure Chests and no Checkpoints. The object is simply to reach the end, though getting there is considerably more difficult than in a regular stage.
Once you clear the tenth stage of a world, you will automatically proceed to challenge the Boss of that world. Each boss is a challenge of figuring out just which Jelly Bean power to use at each of the Boss's different phases of attack.