Generation I set 151 species and 15 types

Ghost did nothing to Psychic in Generation I

• The chart listed Ghost against Psychic as 0 times; Lick was the only damaging Ghost move that used the chart, and the entry is widely regarded as a programming mistake.
• Bug and Poison were each 2 times effective against the other.
• Ice against Fire was neutral at 1 time.
• Psychic types had one weakness, Bug, and the strongest Bug move was Twineedle at 25 power per hit.

One Special stat served attack and defense

• One Special stat covered both special attack and special defense.
• Critical hit chance came from the attacker's base Speed, so Persian and Dugtrio landed far more critical hits than slow species.
• The damage roll multiplied each hit by a random integer from 217 to 255 out of 255.
• Hyper Beam skipped its recharge turn when it knocked out the target.

Training ran on stat experience and DVs

• There was no breeding, no gender and no held items.
• Stat experience rose after every defeated Pokémon, by that species' base stats, up to 65,535 per stat.
• Determinant values ran from 0 to 15 for each stat.
• Four species evolved by trade: Kadabra, Machoke, Graveler and Haunter.

The party, the box and the TM began here

• The six-Pokémon party, the PC box and the 50 single-use TMs date from these games.
• Five HMs taught Cut, Fly, Surf, Strength and Flash.
• Six status conditions applied: burn, freeze, paralysis, poison, badly poisoned and sleep.

Freeze, sleep and Focus Energy worked differently

• A frozen Pokémon stayed frozen until hit by a Fire-type move or cured by an item.
• Sleep lasted 1 to 7 turns, and the waking turn was lost.
• Focus Energy divided the critical hit rate by four instead of raising it, because of a programming error.
• Paralysis cut Speed to 25 percent.

Red, Blue and Yellow split the 151 species

• Red and Blue split exclusives: Ekans, Oddish, Mankey, Growlithe, Scyther and Electabuzz appeared in Red; Sandshrew, Vulpix, Meowth, Bellsprout, Pinsir and Magmar in Blue.
• The Japanese Blue release used redrawn sprites and its own exclusive list, and the international Red and Blue took their code from it.
• Yellow gave the player a Pikachu as the starter that walked behind the player and refused to evolve.
• Yellow made Bulbasaur, Charmander and Squirtle obtainable in one game through gifts.

Type chart era

15 types in the Generation I chart

Battles in these games follow that chart. Open the type chart by era