Starting with Venomoth: One of Kanto's most neglected mons: Honorary early bug mon, but without the attention Butterfree or Beedrill may get, because they do appear earlier to be fair.
All it got was Quiver Dance, like all of its early bug friends, and that's all it needed to climb up there as an above average Pokémon.
Even before that, the Phys/Spec split got it to use its STABs and punch shit hard, or setup Toxic Spikes. 90 Spa & Speed is decent enough to fire off powerful moves when Tinted Lens comes into play.