mimics can teleport and change props, and be killed
mother mimics can spawn babies across the map
there are balloons that spawn naturally

wisps kill you instantly , after you harm them in any way, also immortal?
all anomalies can level up

gravitron,murk and both corrupted tools can be killed
i think the rest are immortal

Unknown will actually move towards you for a moment if you do not move your camera

entities also seem to have some kind of upgrade system, as of what it means im unsure

found out the displacer CAN be killed

unknown can also die

hoarder can die

hoarder can take npcs

hoarder will become aggressive if approached and will grab and damage you slightly

i believe the hoarder and the displacer are heavily tied to eachother, they have the same appearance and both move objects, leave a translucent trail and do so while warping, where the two differ is the hoarder places their props in one location and will attack if the player gets too close, while the displacer simply moves things to random locations without any harming of the player

The catalyst reacts aggressively to flashlights

the harbinger's box appears to unleash various entities all around the map at random

the phantom engine can be restrained with welds and ropes

using the toolgun on a wisp does not count as harming it, so it too can be restrained with welds and ropes