What are some game mechanics exclusive to Generation 1 that you miss?

[Shiny Venusaur]

I wouldn't say that I miss this specific mechanic, but one of the few mechanics that are genuinely unique to Generation 1 is that Body Slam cannot paralyze a Normal Type. When this mechanic was discovered years past RBY, it drastically shifted the RBY meta, which was incorrect on simulators for years since no one had caught this very specific hidden move effect.

Bulbapedia - Body Slam (move)

 

[raichu27]

The item glitch comes to mind. Moves like Pay Day, Bubblebeam, and Mimic being TMs, too.

I don't miss how focus energy lowered your chance of critical hits except in Pokemon Stadium 1. Ghost having no effect on Psychics or Bug being strong against Poison also come to mind.

 

[PCN24454]

The item glitch comes to mind.

Glitches don’t count as mechanics.

 

[pacman000]

If a Pokemon was trapped in wrap or a similar move, you could recall it & try a different Pokemon. I miss that.

 

[Missingno.Fan]

I liked Poison being super effective against Bug. That made perfect sense to me and I don’t know why they got rid of it.

 

[jaden767]

The limited backpack. I liked how what you carried in your backpack actually mattered. You couldn't just hoard everything.

Yeah that made sense at the time. Don't get me wrong it's way more convenient to be able to carry more stuff in the newer games but it's less realistic than it was in Gen 1.