Deep Space Kraken
The Deep Space Kraken is a bug in the game that is experienced in deep space. It is an error with the games physics engine, PhysX, which attacks spaceships as their velocity increases. The number of parts in your ship has a large effect on what speed the Kraken Manifests itself, as well as how much it affects your ship. It primarily causes your craft to go off trajectory due to forces that shouldn't be there.
The cause of this bug is extreme velocity; the bug subtly exists even in Kerbin orbit, though is mostly only noticeably experienced in Kerbol orbit due to velocity you "gain" when you transition SOI to Kerbol. A fix was implemented in 0.17, involving offloading velocity to the universe around you meaning that the focused vessel will always be at a somewhat low speed. However, the same bug under a new name, the space Cthulhu, can break apart ships when quickly warping out of high time accelerations (as of 0.17). It has been reported that Cthulhu can attack ships that are still on the launch pad when coming out of a high time warp.
Gyro Kraken is when a spacecraft will spin around vibrate so intensely that the spacecraft will be obliterated. The rate of spinning is so extreme that it is impossible to be replicated manually.
Warp Kraken is an 0.19 bug that attacks kerbals exiting spacecraft that have just come out of a high time warp. Upon contact with the surface the bug causes the kerbal to be shot out of the solar system at an insane velocity (possibly exceeding the speed of light) while destroying all spacecraft in the vicinity. This bug has so far only been encountered on the Mun and has not been confirmed to exist in 0.20.
Deep Space Cthulhu
Deep Space Cthulhu is a fan-made term for a version 0.17 bug similar to the Kraken, except it only seems to attack when exiting high time warp speeds. Instead of adding phantom forces, Deep Space Cthulhu instead tends to detach parts from one another. In milder, yet more infuriating forms, Deep Space Cthulhu will instead detach small groups of engines, making it impossible to perform orbital burns.
The EVA Kraken is a 0.20 bug that spectacularly destroys a spacecraft if a kerbal on EVA approaches it at high speed. It only occurs in fairly specific circumstances. A kerbal must EVA from a ship and go far enough away that parts physics stops acting on the ship (200 metres). Then if the kerbal comes within 200 metres again at high speed there is a chance the ship will explode in spectacular manner, with the debris shooting off at high velocities (sometimes enough to escape low Kerbin orbit). Sometimes the unfortunate kerbal will be killed as well.
The reasons behind this form of kraken are not well understood. It is possibly due to the parts clipping into each other as physics starts to act, or another theory is that it is due to physics trying to start too quickly to keep up with the rapidly approaching kerbal. At the moment very little concrete data exists. What is certain is that it always starts as the kerbal passes exactly 200 metres from the craft, and that it only occurs when the kerbal is moving at relatively high speeds. The kerbal does not have to come from the ship it destroys. It is unknown what happens if physics starts to act on multiple ships at once.
There are good reasons to take precautions against EVA kraken as it always destroys the affected ship completely. The best prevention tactics known so far is to approach ships slowly and quicksave often.
The Hell Kraken is a form of Kraken which was discovered during the 0.21 version. It seems to strike when a kerbonaut on EVA hits a celestial body's surface, causing the screen to turn black, with the UI remaining though. The altitude will remain at 666 666 m, which earned this type of Kraken its name.
It also stops you from leaving your spacecraft via EVA and makes it impossible to launch or build new vehicles by blacking out the space center.
The "NaN Kraken" is a form of the Kraken which can only be evoked if the orbits of celestial bodies are altered, via a mod or the alteration of the game's code. If a ship is on the surface of a planet, and another planet is suddenly moved so that the craft is within its SoI, the sudden change in gravity will cause the craft to go towards the latter at incredible speeds, and will sometimes even go through a planet to accomplish this. Please note that the gravity of the second planet does not have to be greater than that of the first, though the reason for this is unknown. This Kraken gets its name from one of the many bugs it causes; when this Kraken is acting upon a vessel, its velocity in the Tracking Station will display as "NaN".
Some players might not consider this a form of the Kraken, but rather, PhysX having a strong reaction to extreme conditions. However, it can be considered a Kraken in many respects, since it can suddenly separate a ship from launch clamps, cause launch clamps to disconnect from the ground but remain in their position relative to one another, and will automatically remove any and all connecting struts and fuel pumps, as well as distorts a Kerbal just like the Gyro Kraken and the Deep Space Cthulu.
- (Bug fix) 'Off loading' velocity to the universe alleviated this problem, though it still exists in 'new' format