I think scep is cool enough to be worth keeping around until sometime after Mt. Moon. I mean, other than geodude mt moon doesn't offer much unless you switch Pestilence out for a Paras. And, I'm not sure on this but does Magikarp count as the one mon you get from route 4? I'd just catch one when you get the old rod, prior to that training him seems like a colossal pain in the ass.
Personally, I feel Biolante, Spearow, Pcebro, Scep, Pestilance/Paras, and geodude are good. Unless you get a zubat, in which case 5 is probably good.
I'll probably keep Pestilance due to Paras having two double weakness.
Originally Posted by EspritRequin
Excuse me? I believe you mean when he catches a zubat.
I might find other things in each area. As unlikely as it is.