What determines egg moves to be egg moves?

Question

Question pertains to Gen III only please. If it extends into IV+ just mention.

Been having trouble finding a more proper explanation as to how egg moves work.. and by work, I mean how they're established in the first place.

Are they merely a separate move list that Pokemon have similar to their level-up counterpart where it focuses on the breeding mechanics in order to be obtained?
Or are egg moves some loosely defined moveset that really could change if a Pokemon were to simply have a move it shouldn't in its move pool?

My hunch/assumption is that egg moves are merely some sort of separate hard-coded move list similar to how the level-up moves are arranged for Pokemon. I'm trying to refrain from requesting a ROM's point-of-view, but if that's the case I am all ears. The breeding sections explained in most sites do not explain the little detail I'm trying to clear up in my mind. I guess I am secretly hoping I won't be confined to the usual TM/tutor/egg list you see online.

A secondary/probably the same question to bring up is what DEFINES an egg move? Is it an obtainable non-TM AND non-level up move? If so, then why does Hoppip have reflect as an Egg move and not as a TM-learnable move? Would that then make the definition of an egg move to be ANY move that is available to the Pokemon that isn't found in its level/TM list? As Bulbapedia says:

Egg Moves often (but not always) cannot be learned through other ways.

Even if that were the case- what determines the egg moves to be there in the first place?

Is it hard-coded or not?

Comments

I'm pretty sure that egg moves are simply a hard-coded list of moves for each Pokemon. I have never seen any evidence suggesting it isn't.

As for the second question, I have seen egg moves that are also...
level up moves (Generation 4 Spiritomb shadow sneak)
TM moves that the Pokemon can learn (Generation 4 Torchic rock slide)
TM moves, but the Pokemon can't learn that TM (Generation 4 Heracross false swipe)
tutor moves (Generation 3 Geodude rock slide)

(so yeah egg move lists are kind of dumb) Egg moves sometimes overlap with TM moves and sometimes don't, so I think this is more evidence that they're just hard-coded lists.

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If you really want to know the answer, then I think you should ask some ROM hackers. I think you can find them on a site called Pokecommunity.

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I will be asking ROM hackers later this week but not on Pokecommunity because it's filled with a bunch of nasty people. Youtubers will be a better option and I'll update this comment later with what I find out.

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Egg Moves are a set of moves that a Pokemon can be hatched with, but cannot learn by TM, Tutor, or Level-Up. To obtain Egg Moves, The mother needs to be the species of the Pokemon you want to receive the Egg Moves, and the father must be a Pokemon that can breed successfully with the mother (Ditto does not count) and must know the Egg Moves. The Pokemon will be hatched as the same species as the mother, with the Egg Moves from the father.

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I'm pretty sure this question asks how egg moves are programmed into the games, not what players have to do to get them.
@bubbles If you don't like this answer, then you can ask Fizz or Hellfire Taco to hide it and put the question back on the unanswered list.

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Preemptive, but I'm converting this to a comment. Its first line contradicts what is already established in the OP, which is enough.

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I'm pretty sure its just a move a hatched Pokemon can learn from their parents. For example Morelull and Shiinotic are the only Pokemon that can learn strength sap by leveling up. But if a Shiinotic (or Morelull) breed with someone on the Oddish line (they can learn strength sap by egg move) and the egg turned out to be Oddish, it might hatch with the move strength sap, because it inherited it from its parents. Was that an adequate explanation.

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Converting this to a comment as it's indecisive.

Answer 1

the way it works is if one of the parents have the passable move, like inceneroar being able to pass on fake out to litten, the move is an egg move. its hard coded, so if the parent has a passable move, it will be passed on. this applys to every generation that egg moves are a thing. hope I helped.