What modern type resistances didn't exist in Gen 1?

Question

For example, nowadays Grass/Poison types take neutral damage from Ground attacks because Grss resists Ground. However, in Blue a Diglett's Dig was super effective on my Ivysaur. Is this a bug, or does Grass actually not resist Ground in Gen I?

Comments

That was a bug, http://bulbapedia.bulbagarden.net/wiki/List_of_glitches_in_Generation_I#Dual-type_damage_misinformation
This should help. Should I answer or would you like a more in depth answer?

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It's probably just a bug. I myself have never played generation one games, but I can say that the same has happened to me before.

I had a Spiritomb—a Ghost/Dark-type—fight against a Bug-type; their Bug-type attacks were listed as super effective against my Pokémon, despite the fact that it should have been neutral damage since Ghost/Dark-types have no weaknesses prior to generation six.

Answer 1

These are two damage charts.
- Gen 1
- Gen 6
I'm gonna list some of the more basic changes.
- Anything involving the Fairy, Dark and the Steel type is irrelevant in Gen 1
- Psychic also resisted all Ghost moves in Gen 1, this was a bug.
However, the glitch you witnessed was one of the, shall we say, unique glitches that existed in Gen 1. It happens when a move like Earthquake hits a Pokémon like Venasaur for example. Earthquake hits Poison super-effectively however Grass resists it. This causes an erroneous message to appear. The link explains this more in depth.

Hope I helped!

Comments

So it is a bug. Thanks!

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No problem my friend.