By leveling up:
* Sceptile: Learns Power Whip at level 45.
* Grovyle: Learns Power Whip at level 45.
* Treecko: Learns Power Whip at level 45.
By breeding:
* Bayleef: Can breed Power Whip (requires a parent knowing the move).
* Shroomish: Can breed Power Whip (requires a parent knowing the move).
* Breloom: Can breed Power Whip (requires a parent knowing the move).
* Seedot: Can breed Power Whip (requires a parent knowing the move).
By TM:
* Power Whip is not available on a TM in Pokémon Pearl.
Other methods:
* Trading: You can trade with other players to obtain Pokémon that know Power Whip.
Keep in mind that not all of these Pokémon are available in the wild in Pearl. You may need to breed or trade to obtain them.