Dupe state is a "state" that Jak can enter while performing the duplication exploit on scout flies. Some side effects that occur while in dupe state include seemingly random hardlocks, statue glitch, failure to load certain parts of the game, and collectable entities not disappearing after collecting them. Dupe state can travel across save files, which is a trait not seen in any other known state. This leads some to believe that dupe state is not actually a state.
Using yellow eco while dupe state is active will lead to a statue glitch, where Jak becomes frozen in place right after you press the square button to shoot yellow eco. This is the only known way to consistently perform the statue glitch.
Currently, there is no use for dupe state in any speedruns of Jak and Daxter: The Precursor Legacy.
Water111 had this to say when asked about what could be causing dupe state.
"A lot of the stuff in levels in Jak 1 is a "process". So there is a process for each orb, enemy, animated thing, camera, Jak,..... Each process gets run once per frame by the kernel, and each process has some memory associated with it to store its state (like where the item is located, what animation it plays...). Many processes have their memory allocated manually, like the orbs, which go into a special "collectables" heap. But other things, (like flies which spawn from crates, eco....) go on the "actor" heap. This actor heap has some really complicated code that will move around the memory for processes to compact them together and get larger chunks of free memory. However, this code is really sensitive - if any process using the actor heap accidentally writes past its allocated memory, the engine won't be able to maintain the actor heap any more. This means that deleting actors might not work, or there could be random memory corruption. Some common side effects of the actor heap getting messed up is objects don't disappear when they are supposed to, because they cannot be deleted from the actor heap. Other times, certain objects won't spawn because the actor heap is too full. Or sometimes, when it tries to spawn new enemies, it will just crash because it overwrites something else in the actor heap. I believe in debug mode, it would display "Low Actor Memory" in this case. I am not sure how save data could cause this to happen though."
To activate dupe state, you need to load a save file (without saving) on a specific frame of a spin kick while collecting a scout fly. Once you load back in, the dupe state will be active. It works best on Geyser Rock with the first scout fly you encounter. You are able to load any save file once you have the initial spin kick set up, allowing the state to carry over with Jak to any level you load him in to.
Dupe state was inadvertently found along side the discovery of Precursor Orb, Scout Fly, and Power Cell duplication in Jak and Daxter: The Precursor Legacy, which was discovered by RNGPenguin on January 14, 2018. While other runners attempted to perform the duplication exploit, some of them reported strange side effects when failing the dupe and reloading the save file to try again. These side effects were listed earlier at the top of the page. Two days later on January 16, 2018, Ruh found a consistent setup to cause the strange side effects and coined the name Dupe State.