powerful grass-type and electric-type in Johto ?
Pikachu @Lightball (Kanto, nvm)
Jolteon (You'll get Eevee in Ecruteak, and a Thunderstone in crystal soon after.)
There are good alternatives, though - Abra w/ T-punch, Magmar w/ T-punch, etc.
Bellsprout (Very good alternative)
Oddish ( If you didn't defeat the rockets, its in ilex forest)
This is to beat croconaw, right? sorry