maybe make it charge, the electric attack, instead of nasty plot.. while pichu can learn both, players may be better able to recognize it as a move to power up the next "special attack" (lol, bad joke, get it?) but be a little heavier until then (the special defense boost) ...i always thought pichu or pikachu should have had an electric move that could be charged, but since there aren't very many actual attacks in the game that need to charge, not like solar beam for instance, i sometimes thought about moveset ideas where they used the move "charge" to power up the next attack, whatever it was... technically, pichu learns nasty plot on its own, but it can egg the move charge, so it's not inaccurate...
personally, i don't think there are many available idea for pichu that would make him better than pikachu though
and nasty plot would probably work better, but even then, he's just a first evolve, and not necessarily supposed to be a really hardcore fighter... as a matter of fact, you'd probably have an easier time making a moveset for raichu that's close to pikachu than a pichu that is close in balance to pikachu
...i'm interseted though to see how well this turns out though, and what ideas you may have
sorry i can't offer very many more ideas, but i'll offer some morale support ^^ good luck dood