The entries for both Mew and Arceus purport them to be the first, with Mew being “the ancestor of all Pokemon”, and Arceus as “the creator of all Pokemon.” While this has stumped players since Arceus was introduced in Generation 4, PokeDex entries are known for being unreliable.
For example, two foot tall Pokemon Larvitar has a PokeDex entry which claims it eats whole mountains for a meal. Meanwhile, Magcargo’s claims the snail is 18,000 degrees Fahrenheit; twice as hot as the sun.
However, while these can be chalked up to exaggeration, there can only have been one Pokemon which came first. On Reddit, Ninsunekon thinks they have come up with an answer, but they add the disclaimer that the theory is likely not canon, and that they might not be the first to have thought of it.
Ninsunekon suggests “Mew gave birth to the egg that Arceus hatched from, and Arceus created Mew. Neither of them are first or second, but both of them are first and second.” This theory holds water because of a third Pokemon: Dialga.
Dialga is the Pokemon representation of time itself, and nowhere in any PokeDex entry is there a suggestion that Dialga was first. This means, according to Ninsunekon, that the game exists in a universe of non-linear time.
Before Dialga existed, time did not move forward in a straight line. Because of this, Mew and Arceus created each other; they are both first and not first. Once Dialga was created, time became linear, and so it is clear every other Pokemon was created after Mew and Arceus, leaving those two, simultaneously, as the first ever.
In the comments section, Redditor Karmo has another theory. They suggest that since Arceus is a God, they were the first. However, Arceus’ first successful attempt at creating a living creature was Mew, also making Mew, in a way, the first.
In other Pokemon news, fans have recently discovered a new Easter egg in Pokemon Yellow’s Rock Tunnel.