Evolves from Pikachu when you don't take it to the Pokemon Centre for a long time. It's tail falls off and it acquires a badly drawn look...to the point of having no fill.
A pokemon that evolves into ekans? Well that seems kinda hard, I can't imagine anything like that, sorry. Maybe I could draw a pre-evo of another pokemon that doesn't look so...first state? I don't know how to say it.