Pokemon Gen 1 Type Effectiveness glitches

pokemon-first-generation

I'm watching a speedrun of Pokemon Yellow, and an Oddish used Absorb against a Nidoking. The game indicated that this attack is "not very effective", even though Ground's weakness should cancel out Poison's resistance.

It's been so many years since I've played Gen 1, but I have a vivid memory of my Venasaur's Razor Leaf also being NVE against Lance's Gyarados, even though a Water/Flying type should be neutral against it. I'm not sure how watch it said for Aerodactyl.

What are the known bugs in the way Gen 1 handled overlapping weaknesses and resistances in a dual-type Pokemon? Why does it show "not very effective" for these Pokemon when they should be neutral?

Best Answer

According to Bulbapedia, typed moves against dual type Pokemon (eg Grass vs Water/Flying) do inflict neutral damage, but there is a glitch which causes the 'Not very effective' message:

Dual-type damage misinformation

In Generation I, Pokémon with two types that have a weakness and resistance to the same type receive neutral damage from that type, but the incorrect message is displayed.

For example, Grass-type moves do neutral damage to Gyarados, but if Gyarados is hit by a Grass-type move, the game erroneously states that the attack is "not very effective...".

The 'Not very effective' text caption is triggered by a glitch with the way info messages are chosen and prioritized, which does not respect dual-typing. So for our Grass move v Water/Flying example:

  • Grass v Water is checked 4th -> message is set to 'Super Effective'
  • Grass v Flying is checked 27th -> message is set to 'Not Very Effective'

...Consequently, in this example, the game chooses the message for scenario #27, returning the wrong message "It's not very effective...".

You can read more about the glitch on Bulbapedia

Related Topic