Many species of Pokémon are capable of evolving into a larger and more powerful creature. The change is accompanied by stat changes, generally a modest increase, and access to a wider variety of attacks. There are multiple ways to trigger an evolution including reaching a particular level, using a special stone, or learning a specific attack. For example, at level 16 Bulbasaur is capable of evolving into Ivysaur. Most notably, the Normal-type Eevee is capable of evolving into eight different Pokémon: Jolteon (Electric), Flareon (Fire), Vaporeon (Water), Umbreon (Dark), Espeon (Psychic), Leafeon (Grass), Glaceon (Ice), and Sylveon (Fairy). In Generation VI, a new mechanic called Mega Evolution—as well as a subset of Mega Evolution called Primal Reversion—was introduced into the game. Unlike normal evolution, Mega Evolution and Primal Reversion last only for the duration of a battle, with the Pokémon reverting to its normal form at the end. Forty-eight Pokémon are capable of undergoing Mega Evolution or Primal Reversion as of the release of "Sun" and "Moon". In contrast, some species such as Castform, Rotom, Unown, and Lycanroc undergo form changes that may provide stat buffs or changes and type alterations but are not considered new species. Some Pokémon have differences in appearance due to gender. Pokémon can be male or female, male-only, female-only, or genderless.