There are 17 Pokémon types total. Each type has different weaknesses and resistances.
Fire is considered to be an offensive type. Many fire type moves are high powered and most fire type Pokémon have a high offensive stat but have low defensive stats.
Water is usually considered a defensive type. A majority of water type Pokémon have high HP and defensive stats. The most common form of attacks from water Pokémon are Special Attacks.
Normal type Pokémon are extremely versatile, varying extremely from one another. Normal types usually have large move pools.
Steel type Pokémon usually have great Defense or Special Defense. Steel types have many resistances so they are quite useful. Steel is a poor offensive choice, however, as many types resist it.
The Electric type is considered to be a poor defensive type as it is weak to the common Ground type moves. However, Electric Pokémon usually have high Speed and have a high offensive stat to hit with.
Dark type is a generally bad defensive type, but is an average offensive type. Dark Pokémon are almost always strong attacking Pokémon.
Bug type is a poor defensive type due to its common weaknesses, however most Bug type Pokémon have another type which cancels out many of them. Bug type Pokémon are usually fast and strong or slow and sturdy.
Psychic type Pokémon are usually very fast and strong. The Psychic type is a decent mix of both offensive and defensive Pokémon, and home to many of the Pokémon that are in the Uber Tier of Competitive Battling.
Fighting type Pokémon have high attack and many have decent defensive stats. The Fighting type is a good offensive type, hitting many Pokémon hard. Defensively, the Fighting type is decent as it has resistances to some common offensive types but is weak against the semi-common Psychic and Flying type moves.
Physical and Special
In previous generations, physical and special attacks were separated by type, but starting in the Generation IV games Diamond and Pearl, they were split into more logical categories. This brought great change to the metagame.
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