User blog comment:Bobdave/Lapras vs Gastrodon. Rap Battles of the Pokédex Season 1/@comment-3401602-20160511125915/@comment-4490782-20160511135202

You erase a bit of the base of the thing you wanna reflect with a soft brush so that the edges fade out. Then you go over with a half-opacity brush so there's more of a transition. Duplicate the required layer and horizontally flip it. I used the perspective tool a little but you don't have to. Then I lowered the opacity until it looked good and added a wave distort filter (ripple also works).