At least one species of Pokémon evolves at every level from 20 to 40, except at levels 29 and 39
Steel Pokémon are immune to Poison attacks, but can nonetheless be poisoned through the Poison Point ability or Beedrill's move Twineedle.
In R/B/Y , a dual-type Pokémon being attacked by a move that is super effective on one of its types, and not very effective on the other, will take normal damage. However, R/B/Y displays "It's super effective!" or "It's not very effective..." message anyway.