Dark typed Pokémon were introduced to help balance out the types, particularly by being effective against Psychic Pokémon. When paired with a Ghost type it is the only type to have no weaknesses. Dark moves are super-effective against Psychic and Ghost, but are not very effective against Fighting, Dark, and Steel. Psychic Pokémon have no effect on Dark types and Ghost and other Dark types have little effect. Fighting and Bug Pokémon are super-effective against Dark Pokémon. Despite being introduced late there are still 70 different Dark Pokémon.
Here is a list of some of them:
Poochyena have a very keen sense of smell and will bite at prey tirelessly. But if the prey fight back, Poochyena often run away. Mightyena work in perfect coordination to bring down opponents and are very loyal in nature as they follow a pack leader on instinct.
Purrloin can stand on their hind legs and walk around, and they have a liking for stealing things. They are very charming and cute, and use this to their advantage. Even when caught taking things red handed, they often get away with it because of their charm. Liepard are very attractive Pokémon that can appear and disappear at will. They use this stealth to track down opponents and attack them before they expect it.
Zorua can take on the appearance of other Pokémon, but unlike other Pokémon that use Transform, it does not pick up their moves, it merely looks like them. When transforming into a human, it keeps its tail, and will untransform if it is pulled. They often laugh at opponents, and even when they are caught up to mischief they will often still laugh at those who caught them. Zozoark lose their ability to Transform, but they can create incredibly convincing allusions that can even fool cameras. These allusions are so strong that sometimes other Pokémon will feel as though they have been physically attacked even when no real harm has been done. Zoroark live in packs where unity is strong and will keep their Zorua young in their manes to protect them.
Grimsley
Elite Four
Unova
Karen
Elite Four
Kanto or Johto
Steel Pokémon were also introduced in the second generation, and have the highest average defense stat in the game. 11 types are not very effective against it, and Poison has no effect, so the other types that do well against Steel Pokémon are Electric Types as well as Fire, Fighting, and Ground which are all super-effective. Steel moves are super-effective against Ice and Rock Pokémon, but are not very effective against Fire, Water, Electric, and other Steel Pokémon. This type has 71 Pokémon, some of which are discussed below:
This family of Pokémon are genderless and Klink is formed of two bodies that cannot join with anyone else or they will become separate. Klang attack opponents by throwing tiny gears at them and communicate by turning their gears. Klinklang can recharge itself by spinning its red gear.
To make its body, Aron eat iron ore that they dig up in mountains, and have been known to eat bridges and railroads while it tries to grow. Lairon nest near mineral water and eat rocks that contain iron to build up their strength. Aggron are very fierce and aggressive Pokémon that will claim entire mountains as their territory. If their territory is destroyed from a fire or flood they are known to bring back in top soil and start planting trees and plants to regrow it.
Beldum are extremely limited in battle as they do not have many physical moves at their disposal. This family of Pokémon is said to be related to the Magnemite family, but instead of being electrically based they are Psychic. Metang is made up of two Beldum and can now attack more effectively. They can also fly at up to 60 mph. Metagross are made up of four Beldum and have four brains because of it so their intelligence is very high. They are very vicious in attacking their prey and some are very territorial.
Jasmine
Olivine City Gym Leader
Johto
Byron
Canalave City Gym Leader
Sinnoh