How can a creature evolve to have two separate food cycles?

Question

A species of interdimentional predators exist in a separate reality from ours. They pass into different realities through portals which occasionally open up between worlds. Once there, they feed on the populace for a period of time, before returning to their reality to hibernate. The feeding cycle revolves around feeding off the emotions of young children, and takes place in two cycles.

The first centers around feelings associated with hapoiness. The creature takes the form of an individual meant to inspire love and joy among children, such as a beautiful female caretaker that travels on a flying umbrella. The being would do anything it took to inspire joy in these kids, such as sing along musical numbers, dancing, and making them feel good about themselves, all the while feeding on their emotions. When it has filled itself, it leaves to hibernate for 25 years.

It's next cycle involves feeding on emotions associated with terror. The creature takes a more sinister form, such as a scary looking clown. It works to inspire feelings of fear and horror in it's targets, such as showing them their worst nightmares or painful memories. This can take place over a certain period, until the victim has experienced a suitable amount of fear. Then the creature devours them alive. It then returns to stasis after its cycle finishes, until it's next cycle begins again.

These two feeding cycles are completely different and involve feeding of opposite emotions. These creatures must switch between these emotions after they come out of hibernation every 25 years. Why would a species evolve in this way?

Answer 1

The same way as a caterpillar feeds off of leaves before it metamorphoses into a butterfly to feed off of nectar. Perhaps this 25 year hibernating period is actually part of the creature's life cycle where its entire body undergoes some sort of change causing them to consume the opposite emotion. You can then have a difference between "young" and "mature" creatures.

If the creatures are fairly intelligent, then it could also be more of a preference/ritualistic reasoning rather than pure biology. Maybe they have the power to feed off of any emotion, but they alternate between positive and negative emotions due to some cultural or preferential reason.

Answer 2

because they're actually the same to them and to reduce competition

These emotions might seem contradicting for the creature to need, as their natures seem to be opposite, but that's just from our perspective. In reality, terror and happiness are 2 intense emotions that have been a part of our lives since before the first humans. Sure, they require completely opposite strategies to be acquired, but energy is energy. It's truly not that different from our differences in growing fruit trees and livestock. They seem like opposite things (one is usually fixed to the ground and produces its own food while the other is mobile and can't produce its own food), but we don't care, we need both so we eat both, despite them needing different kinds of attention. In addition even if they're actually opposite to the creatures as well, we need a wide array of nutrients and vitamins, with some being exclusive to animals or plants, so for your creature to require 2 different kinds of energy to remain healthy is far from a stretch, they're simply their parallel universe equivalent of an omnivore.

Additionally, they might eat 2 seemingly opposite kinds of emotions likely due to less competition between creatures which appeared at different times. This isn't a crazy concept, as we see it widely in insects that possess a larvae stage undergo metamorphosis, with the adults usually having a diet completely different from their young, meaning no competition between generations. Even vertebrates like dunkleosteus had such strategies, with the young preying on softer bodied prey while the adults hunted creatures with tougher shells (including their own young, but that's not the point here).

With these opposing feeding periods, newcoming creatures won't compete against the ones who already gone through the transition. The Mary Poppins has already turned into the boogeyman to haunt the kid at night, so a new Mary Poppins can take the vacant place during the day. Yes, once the kid dies the new Poppins will need to find another kid, but since the child can produce both emotions, 2 creatures might be able to feed on the same child simultaneously, so long as they're in different feeding stages (in this case, much like dunkleosteus eating its young, the terror caused by the older creature might hinder the newer one).

Answer 3

The possibilities are nearly endless: Every possibility where there is a duality gives a reason. Here's just a sprinkling.

• Gender: Perhaps good and evil are the equivalent of genders for this species. In order to be able to reproduce, an individual must consume the appropriate energy. They become neutral once the energy has been fully absorbed, and reverse gender with each reproductive cycle.
• Balance: Only creatures with no discernable good or evil are able to cross the dimensional barrier. An entity that always feeds on good or always on evil has a clear charge, even after all energy is consumed. To assure their ability to transit again to feed the next time, they must reverse polarity.
• Practice: Harvesting joy or fear takes skill. Entities switch which they use with each cycle, so they keep their skills up. Too much of one causes the entity to be incapable of harvesting both, so they transition into being either demons or angels. Then when things are too good or too bad, the specialized being starves.
• Faith: These beings exist in a realm between good and evil, carefully avoiding any appearance of making a choice. To show a clear preference of one for the other would shift the spiritual balance of power. The forces of good and of evil must be kept in careful check or the universe (and thus their feeding ground) will be ruined. After all, angels can out-compete for joy, and demons can outcompete for evil.