Shards

Some people have very little connection to their shards. Look at Leet - his shard actively sabotages him. Look at Echidna, or Sveta. You end up with disconnects, and stuff starts to stand out as the shard's behavior becomes more distinct, either in 'episodes' or a pattern of the power not cooperating. —http://forums.spacebattles.com/posts/12852536
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Beyond that, other influences include the passenger playing fast and loose with the power itself, as it controls the metadata, which may be more visible if the subject breaks from their norm in terms of consciousness (gets a concussion, tranquilized), working off base instincts and impulses like 'stay camouflaged' (be a little more creepy and unsettling), intimidate/dominate (passenger works behind the scenes to make you look a little more dangerous as you mutate/grow/surround yourself in the aura of your power), etc, etc. In more pronounced cases, the power is just plain controlled by the passenger, not the host, and the passenger makes the seemingly random or uncontrolled aspects generate more conflict... pushing a power to kill rather than leave someone alive, or a thinker power turns up a vision of something the subject didn't want to see. —https://forums.spacebattles.com/posts/15026557/