Giga Drain / Baton Pass / Agility / Toxic Spikes
This might be tricky to do. You'll need a male Beedrill from Pokemon XD, which has the special move Baton Pass. Beedrill learns Agility andd Toxic Spikes by levelling. So breed those three onto Venonat. Then TM it Giga Drain, then transfer to Gen V and breed with another Venonat!