The ralts line can be safely bathed with soap, as that can easily be washed off their skin. Just be sure to get all the soap residue off and follow up with coconut or baby oil (or simply a moisturizer for humanoid pokémon) to avoid drying out your ralts’s skin.
All bird pokémon, meanwhile, should only be given a water bath at most. That is, it’s important to give many of them a bath consisting only of water at a temperature they can stand. (Rowlet is among the pokémon that need such a bath, but there are a select few, such as the torchic line, that will need a sand bath instead. That would be just an outdoor shallow pit filled with sand or dust.) Water baths not only help a bird wash off excess oil and dirt, but the temperature and the act of splashing or soaking helps them maintain peak mental health—that is, it’s just as relaxing for them as a bath would be for us. It’s just that soap can dry out the skin too much by stripping away all of the natural oils of a bird’s skin, not to mention it can be difficult to completely remove from a bird’s feathers.
Finally, never bathe a buneary unless they can’t bathe themselves (and even then, only bathe a buneary if they’re very clearly in need of a bath) or if they’re covered in something that would be toxic to them. Members of the buneary line bathe themselves (like cats and feline pokémon), and if dampened and not properly dried, a buneary’s soft fur and tufts can grow mold. That and a bath can be traumatic for them.
Actually, the same (never bathe them unless they can’t bathe themselves or get into something toxic) can be said for skitty and all other feline pokémon, but the concern there is less about their health as it is yours. Feline pokémon are generally very adamant about their hatred of baths.
Best of luck concerning your team, anonymous!
Edit: This post now includes information regarding the skitty line (and Bill will, in his words, be “adequately retrained in basic reading comprehension skills”). Thank you for your patience! —LH