I saw this refection technique used on several cards and I was intrigued by it. Believe me, it's simple. Stamp your image on your card as you wish. Next take a piece of acetate and lay that over the image. Stamp again using the same type of ink, color, etc. Carefully pick the acetate up rotate it so image is upside down and flip it over (ink is now on the underside). Carefully line it up and press down. I used a bone folder to gently rub the ink into the card. Lift up and the reflection is made.
Stampin Up Wetlands goose & cattails
Altenew Obsidian Black Ink
Olive green ink for grasses
Altenew Cool Summer Night mini ink cubes for sky & water. Hard to see but the image is on black cs which is on deep blue cs.