GK Wheelerさんのイラストまとめ

Actually, I forgot one. This is my favorite.
Audino could cause mental regression using "Simple Beam."

I like to imagine a Pokemon Breeder, comes home, changes into his AB clothes and asks Audino to use Simple Beam to spend a nigh in playing.

Lastly, for today, there's Xernias, who can't actually regress people, but it can cause "Age Stasis" which would be significant if you met it between the ages of 5-10 years old.

Misdreavous can cast powerful illusions, while the "dream dust" coming from Musharna can make nightmares become real.

Just about any psychic pokemon could cause mental regression. Popular picks would be Gardevoir and Hatterene.

I think I'll use Wednesdays to post my favorite works that are not my commissions.

This is one of my favorite pics ever, done by @laserbeambkk. You should follow and support him if you aren't already.

Lastly, special mention goes to Deoxyz, who could rewrite your DNA and turn you into a SpaceBaby like in 2001 Space Odyssey. (Plus Arceus, obviously)

Maybe Magerna just has a regression beam built into itself.

Maybe Diancie could do something, I just can't think of what.
I got a crazy idea for Hoopa. What if it doesn't actually regress people. What it can do is SWAP you with a younger version of yourself. Stealing baby you from the past, and causing present you to disappear.

I don't think Victini or Keldeo could regress you, but Meloeta could sing a lullaby that turns you into a baby.