In Bastion, shedding memories of life can result in dangerous creatures known as manifestations. As the Kyrian shed the burdens of their past lives, physical manifestations of their tormented thoughts are expelled from their bodies. Only by striking them down can the Kyrian cleanse themselves and achieve ascendance. Manifestations carry great power within them--power that may be purified and used in creations at the Eternal Forge. The echoes of fallen kyrian are also considered memories of that person, and while they sometimes continue serving in the ways their soul did in life, it is best to lay them to rest.
In Revendreth, manifestations are the result of unresolved issues made manifest in the process venthyr used to extract anima as well as produced when souls in Revendreth are unable to be tended to. These entities are dangerous if left unchecked, and must be purged by Stoneborn regularly.
In the first Bastion preview after BlizzCon 2019, they were called manifestations. In the second preview shortly prior to the Shadowlands alpha, their name was changed to memories while retaining the same description. In the game, both names are used.
In the Endmire and Catacombs of Regret, you can see Devourers latched onto some larger Manifestations. Given they feed on anima, and even though Manifestations are byproducts of anima extraction, it implies they are still made or contain anima.