[This is an expanded/refined version of my old question: How would animals adapt to darkness-made beasts? ]
Premise: 'Beasts'/Seraphins are other-worldly intangible beings (you can't touch them, but they can touch you) that appear and reside within our world's dark places (caves, basements (if unlit) and the general wilderness at nighttime etc.) However, when exposed to some (depending on intensity) light, (only parts exposed to light, e.g., if only the arm is lit, only the arm is tangible.) They turn tangible and can be killed/harmed. However, it is very very unlikely that they will willingly stay tangible and so will avoid light as much as possible- they fear the light, in a way, as it makes them vulnerable and susceptible to harm.
They seek our 'dark places' as their own dimension is always unbearably bright- so much so that not only does it disable their incorporeal abilities; but also puts them in constant agony. There is no single surface/crevice/area in their home dimension that doesn't emit said 'blinding light'. However, they can open dimensional 'slits' that allow them to slip into our dimension- where darkness is quite abundant.
Information on 'Seraphins'
- Seraphins appear as semi-humanoid creatures that are invisible to the human eye save for infrared viewing devices, ie. infrared goggles, scopes, etc. as they do emit infrared radiation. Concept: [Credit to: Thomas Istepanyan @Artstation]
The main idea is that they look semi-humanoid ie. example/concept given above- but more on the colourful side. They also have human-ish features akin to 'Titans' from Attack on titan where they go into the realm of the 'uncanny valley'.
Consumption- Seraphins do consume food- mainly animals and humans, if given the chance. Sea creatures or any creature submerged in water is an exception- they cannot enter water. (Though if a building was underwater and was unlit, they could 'slip' into it.)
Behaviour-Their main behavioural patterns is akin to that of the previously mentioned 'Titans' (Attack on titan) where they wander aimlessly seeking food, though they will ignore prey if they are 'full'. The Seraphins are quite common- You might encounter 5-10 if you are in darkness.
Danger- Very dangerous mainly due to their inherent intangibility, most animals (unless they emit light.) can't interact with them, and humans (without light.) Can't either. Because of this, if you are in the dark you are pretty much already dead if a Seraphin takes an interest into eating you. No creature really presents it any danger- excluding animals/humans who emit light and other Seraphin. However, even if you manage to make it corporeal, if it feels in danger in any way whatsoever- they're dastardly hard to kill. If, in their corporeal form, put into the food chain, they would definitely be the apex of apex predators- A dog, wolf, bear or even a couple of lions will have a very hard time killing it- if it doesn't kill you first. In danger, it can move surprisingly quickly- think maximum human capabilities. Their attacks consist of human-esc grabbing, hitting, biting and clawing.
Guns and well-made melee weaponry eg. Spears or swords (if used with skill) can be enough to kill one, though more than one human taking it on would be advisable.
- While Intangible- Light. to be exact, if you can read in said light comfortably without straining your eyes, it should be enough to deter them (turn them tangible.).
- Water- they cannot enter water, though they are not hurt by it. (throwing water on them when they are tangible wouldn't be effective.)
- While Tangible-
- Fire (like many other creatures)
- Starvation (if kept tangible 24/7 and not fed)
- Mutilation/loss of blood (In this case, a golden ichor-like liquid)
Basically anything that will kill humans and animals, though in some cases eg. pure blunt trauma, just on a higher scale.
Question: How might Fauna (animals) adapt?
Could organisms (excluding plants- though they may also evolve to form a symbiotic relationship with some animals) adapt to emit light or would they have to rely on lantern/torch/floodlight/electrical light produced by humans for survival?  More specifically, evolution leaning towards bioluminescence/chemoluminescence in plants and animals, Even more specifically just animals in general, ie. Predators and Prey (by this I mean if you talk about bio-luminescent defences for prey, for example, 'prey' will be an umbrella term for all prey) - nothing too specific like a whole species/family.