The original Pokemon titles on Game Boy had some issues with balancing, particularly in their first iterations Red and Green. Psychic-type Pokemon like Alakazam were a nuisance given the typings meant to have an advantage weren't well thought-out. Many Generation 1 Bug-type Pokemon were weak, and the only Ghost-types were the Gengar line — whose half Poison-typing made Psychic moves super effective. One of the solutions to this problem in Generation 2 was the introduction of Dark-types.
Dark-type Pokemon are immune to Psychic moves, and deal super-effective damage to both Psychic and Ghost Pokemon. The only Dark-types introduced in Gen 2 were Eevee's evolution Umbreon, Murkrow, Sneasel, Tyranitar, and the Houndoom line. They've become more prominant over the years, with Pokemon Black and White introducing a number of monsters including the Bisharp and Mandibuzz lines. The latter is particularly interesting, as the vulture-like Pokemon and its pre-evolution Vullaby have fit a few niches across their decade of existence.
The Lore Behind Vullaby and Mandibuzz
Both the "Diapered Pokemon" Vullaby and the "Bone Vulture Pokemon" Mandibuzz are Dark/Flying-types, meaning they are weak to Rock, Electric, Ice, and Fairy attacks. They belong to the Flying egg group, but are unique in that the entire species is female. This is just one piece of evidence for the evolutionary line being a counterpart to fellow Unova region Flying-types Rufflet and Braviary. Those bald eagle-inspired Pokemon can only be male, and both Rufflet and Vullaby evolve upon reaching level 54.
While one could consider this a Pokemon universe equivalent to the kind of sexual dimorphism displayed by real-world cows and bulls (a phenomenon emulated via the Pokemon Tauros and Miltank too), it mechanically leads to Vullaby being exclusive to Pokemon Black as Rufflet is exclusive to White. The sequels Black 2 and White 2 also have events related to the duo, with either a Mandibuzz or Braviary that have their Hidden Abilities appearing on the overworld in Route 4 during certain days of the week.
Various games' Pokedex entries offer explanations for the bones in Vullaby and Mandibuzz's design. Pokemon Ultra Sun says Mandibuzz offer the skull-shaped bone diaper to Vullaby so it can protect its rear, as the base-stage evolution can't fly with its tiny wings. True to life, the baby bird is still a scavanger that sometimes attacks prey in order to replace its bone armor while growing bigger. A few of Mandibuzz's Pokedex entries suggest Cubone are a preferred source of food and their bones are primarily used to construct nests. However, some fans have pointed out that combining the cranium and jaw skull coverings on Vullaby and Mandibuzz creates the head shape of an unknown creature.
Vullaby's Modern Infamy
Mandibuzz has never been the most powerful in competitive formats, but it is a solid defensive wall with a lot of support-based moves that make it a good option on multiple teams. Its highest stats are HP, Defense, and Special Defense, and its primary ability is Big Pecks; protecting it from Defense debuffs. Trainers could run it with Overcoat, which protects against weather effects like Hail, but it could also be run with its Hidden Ability Weak Armor (which lowers Defense but sharply raises Speed on every physical hit).
The Dark/Flying-type does have a wide movepool to support allies, lower enemy stats, or chip away at enemy health. It naturally learns moves like Tailwind, Whirlwind, Attract, Defog, and Toxic, and can raise its own stats with moves like Iron Defense and Nasty Plot. However, nowadays people may know this evolutionary line more for Vullaby's appearances in Niantic's Pokemon GO. The AR mobile game's November 2021 Field Research has some fans upset because it offers Vullaby as a Research Breakthrough encounter.
It isn't the most surprising choice given Pokemon GO is currently working on adding Generation 5 and 6 monsters, but players have pointed out that Vullaby is a frequent appearance in 12km Eggs. There is a larger conversation to be had about whether 12km Eggs are worth the effort put into hatching them, but either way many seem to agree Vullaby is an underwhelming Research encounter because of its presence elsewhere. At least this vulture of the Pokemon world has some history backing it up for longtime and new fans to appreciate.