Memory Parasite

The Parasites are a shapeshifting species which, according to Rick Sanchez, enslave other races by infiltrating their societies, assuming a form which allows them to blend in while also telepathically altering the memories of those around them, preventing anyone from noticing discrepancies in their cover stories or even anything strange about their usually nonsensical disguises.

However, their ability to fabricate false memories is limited. As theorised by Morty Smith, Parasites are incapable of creating negative memories of their personas, only positive memories. This was quickly proven by Rick and his family as they slaughtered the parasite infestation in their quarantined house, identifying who is a Parasite or not depending on if they are able to recollect any bad moments with them.