The Ekans Line
Did you guys know that Ekans is snake backwards? Woah! Crazy right? Anyway, I kind of love Ekans a little. It just looks so... doofy. I know the anime tried to make it intimidating, but its big toothless mouth and wall eyes just makes it look quite silly to me. There's not a whole lot special to Ekans though, it's really just kind of a big purple snake. But that's okay, sometimes that's all a Pokemon needs to be.
Similarly, Arbok is kobra backwards! Mindblowing stuff here, folks. Arbok I like a little less than Ekans... It just loses all its cute dumbness and turns into a rather generic-looking snake instead. The most interesting thing about it is the pattern on its hood, which changes with whatever region it came from. That's fairly interesting, actually. It's like a regional variant before there were regional variants.