Oh, one more HUGE problem I'm noticing with this topic.
There's a LOT of times where people are saying things like "Gyarados resists grass" or "Bulbasaur resists ground". This is NOT true. The resist message pops up in game yes, but this is a bug and damage is calculated the same as it is in every other generation.
The same goes for when it says that the attack is supereffective but the secondary type resists it. You're actually doing normal damage, not two times damage, despite the games' assurance that you are. This is a well known, well documented bug.
Honestly I'm kind of surprised that a topic dedicated to 1st generation games has missed this completely.
In short, someone needs to go through the whole OP and make sure all the type match ups are correct. Venusaur does NOT resist ground, Gyarados does NOT resist grass, Nidoqueen/King do NOT resist grass and are NOT weak to Bug. Etc. etc.
Here's the bug on Bulbapedia, and I can confiirm it from extensive generation I experience that it is correct.