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 can evolve into Ivysaur. Most notably, the Normal-type Eevee can evolve into eight different Pokémon: Jolteon (Electric), Flareon (Fire), Vaporeon (Water), Umbreon (Dark), Espeon (Psychic), Leafeon (Grass), Glaceon (Ice), and Sylveon (Fairy). In Generation VI, the games introduced a new mechanic called Mega Evolution, as well as a subset of Mega Evolution called Primal Reversion. 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. 48 Pokémon can undergo 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, which 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 of an unknown gender. The Pokémon franchise is primarily intended for younger players. However, each Pokémon has various complex attributes such as natures, characteristic traits, Individual Values (IVs), and Effort Values (EVs). These are intended for people "who enjoy battling and want to go more in depth", according to Game Freak Board Director Junichi Masuda. These individual statistics were also included, because the basic concept of the franchise is to train one's Pokémon. Designer Takeshi Kawachimaru stated that IVs and EVs "help to make each Pokemon in the game individual", as it adds unique aspects to them. Each Pokémon game introduces a few "Legendary" and "Mythical" Pokémon that are powerful, rare, and hard to catch. Pokémon Sun and Moon introduced "Ultra Beasts", which are described as "beings from another dimension" that appeared in the Alola region and are similarly powerful and rare. Design and development Throughout development of Red and Green, Ken Sugimori, a long-time friend of Tajiri, and a team of fewer than ten people, including Atsuko Nishida who is credited as the designer of Pikachu, designed all Pokémon. By 2013, a team of 20 artists worked together to create new species designs. A committee of five people determine which designs are incorporated into the games, with Sugimori and Hironobu Yoshida finalizing the look of each creature.