In LittleBigPlanet (Media Molecule, 2008), every block, joint and piston in a level is simulated all the time, in three flat layers. Dave Smith, who wrote the physics, called it two and a half D, but really 2D. And players build things no physics engine can solve: squeeze a block between two pistons and it can't be in two places at once. An engine that keeps pushing harder every frame ends with things spinning and the whole world exploding.

Smith's answer, from his 2009 GDC talk: on every contact and joint the game keeps two numbers over time, how hard it's pushing and how wrong it still is. If both stay too high for enough frames, it destroys the object causing the trouble, and the rest of the level settles. Better to lose one block than let it get worse, and the builder can see which part broke, rewind and fix it. His name for it: "the slightly brutal solution".

The diorama, the pistons, the crate, the gauges and every limit in this film are our own simplified version, built in code; the real limits were never published.

What should we cut open next in a game you build in?

Sources: Dave Smith, "How Sackboy Learned to Love Physics", GDC 2009 (GDC's recording) and Gamasutra's report the same day; Alex Evans and Anton Kirczenow, "LittleBigPlanet Post Mortem", SIGGRAPH 2009.
Not an official LittleBigPlanet video. Not affiliated with Media Molecule or Sony Interactive Entertainment.
Sounds and music: our own, made in code.