The Displacement Event

[Fate]

Being Shifted affects different characters in different ways. There is no standard for Shifting, no set feeling or sensation that happens to people. There are, however, several commonalities that are known to occur to most Shifted.

• Shifting is painless. The actual experience itself causes only minor discomfort.
• Shifting is disorienting. You are changing from one reality to the next; the laws of physics are changing for you.
• Therefore Shifting can cause some memory loss. This can be as minor as forgetting certain details or as major as complete amnesia.
  
• Shifted only carry through inanimate objects that were on their person at the time. No living objects, including pets, familiars, or other such beings are taken. The only exception are creatures that are fused together on a genetic level, and these are often separated unless the Shifted cannot live without them.
• Some Shifted have described passing through a "neutral zone" that seems to be either an open void or a swirling vortex of colors.
  
• Shifting changes physical appearance in most cases; only the extremely magical or those that are transferring from fantastical creature to human keep many of the exact physical traits.
• Shifting is very likely to occur when a Shifted is attempting to cross realities, dimensions or planes within their own canon. Many Shifting events seem to be directly tied to any such incidents and latch onto them.
• Nobody really understands how Shifting works or what causes it.
  

[Fate]

Regarding metahuman abilities, science and magic

The act of the Shift plays merry havoc with anybody's supernatural abilities. Ordinary humans will be somewhat drained and tired immediately after the Shift, although beyond that they won't notice any significant differences.

The Shift essentially resets everyone at nice, neutral human level. From the beginning, the Shifted are 100% human, even if you were vampire, pony, robot, or what have you. If they have metahuman abilities, they will find that they are severely limited when they first arrive. The longer they remain in Tenebrae, the more of their former abilities they will find returning to them. Physical abilities are recuperated marginally faster - enhanced strength, senses, that sort of thing - whereas mental abilities and those of a more esoteric nature will be regained more slowly. It would take several months or even years for a metahuman to get back to their original level of ability. Sometimes, they won't even come back at all, as they can be blocked by this world in one form or another. Look on the bright side: you lost all the negative side effects too.

Magic users will find similar difficulties. Those people for whom magic is innate will experience the same sort of drop in power, which again will slowly build the longer they stay. Magic is a lot more unpredictable in Tenebrae and a lot harder to accomplish, each spell is two or three times more difficult to achieve than it would be where the Shifted is from, and spells are a lot more prone to going wrong. Magical accidents are common, so it is advisable to exercise caution when spellcasting.

Science works in accordance with our universe's physical laws, any Shifted attempting science that correlates with any laws of physics different to our own will encounter similar difficulties to magic users, if their experiments work at all. Those with advanced scientific ability may be able to recreate technology from their own world, providing they aren't using any materials alien to Earth.
Please bear in mind that they must have the correct knowledge to be able to do this - just because you know how to fire a ray gun doesn't mean you can build one.

Finally, those with particularly advanced knowledge may find some difficulty recalling all of it. Similarly to how the Shift can take some people's memories, it can cause people to forget some things they've already learnt.

To put it in more basic terms, the Shift effectively 'levels down' your character on arrival.