Companions or cohorts in the original LittleBigPlanet usually revolved around the use of the enemy brain (with it's simple walk-to/run-away mindset) or invisible pistons/switches and stickers to simulate a person (like the Creator Curators).
LittleBigPlanet 2 introduces a new way to create these friends or foes. They're called Sackbots! A Sackbot by default looks like a squarish Sackboy without a face, like a puppet or marionette. But, adding a costume to the Sackbot allows it to look like a regular Sack-person (or a super deformed one).
Additional tweaks allow the creator to change the Sackbot's physical size, set the way the Sackbot acts (like a robot) or even record an animation, choose weak points, set on fire or electrify to hurt Sackboy, even set if its scared of heights.
The best ability, is allowing the Sackbot to be controlled by the Direct Control Seats. Allowing things like giant robot battles or fighting matches with another Sackbot.
Lastly, Sackbots can be friendly companions. When setting the Sackbot to follow you, they would even get in vehicles with Sackboy.