>>22153225This.Mega evolution is pretty much just a gen 6 thing. Odd numbered gens still have not produced cross-gen evolutions, whereas the focus in even numbered gens has been and still is the introduction of new evolution methods and new Pokemon to abuse them. Incidentally, they also always include a new Eeveelution. Odd-numbered gens outside of gen1/FRLG obviously, thus far, have not even had Eevee in the region dex.
Gen 1: Introduced eevee, stone evolutions
Gen 2: introduced Held Item evos, happiness evos, daytime evos. Two Eeveelutions.
Gen 3: Only cross-gen mons are Wynaut and Azurill. One was likely intended for gen 2, the other is a lazy copypaste of Cleffa
Gen 4: Half the dex is cross-gen evos. 2 New eeveelutions based on the Location mechanic that still only 2 other pokemon use. Unless you count Sliggoo i guess.
Gen 5: No cross-gen pokemon whatsoever. As such, no eevee. However, Wild Eevee appear very rarely in the sequels. This is stated to be a result of importation, and likely the wild Eevees are the stray offspring of the pet eevees that live in Castelia, hence only appearing in the park in that city.
Gen 6: 40+ mega evolutions and counting, plus Sylveon. Also, Eevee is found alongside version exclusive dog-mons (Houndour/Electrike) and introduced the aforementioned Sylveon. Much like Glaceon/Leafeon before it, no other Pokemon uses Sylveon's evolution mechanic, which will probably be forgotten in later games and remain unused for any other 'mons.
