It's fun to make a themed night light in any style you choose.
You will need:

A cardboard craft box approx 5x5 or smaller
Plastic window (can be table cover cut to shape)
Hot glue
Paper cutouts (mermaid, treasure chest, or any other design)
Craft sea grass, shells
Paper flowers
Pompom ribbon
Acrylic paint
Sparkle paper
LED night light
jute ribbon

For each night light it is the cutting and gluing of all the parts that can be tricky. The easy part is embellishing in your own style.
I will post a tutorial on how to attach the plastic window and the LED light and how to create depth for the paper cutouts inside and how to affix everything so that it does not fall apart.
These night lights handled carefully will last forever.
You can make them as simple or as elaborate as you choose and have fun with any theme!

A bit of glare with my camera but this lights up really nicely.

Hello Kitty is light plastic and hollow, her companion is a paper cut out along with a row of colorful paper trees and houses in the background to make it funky and fun.

This is a simpler and easier to make design. Just a lot of pink kitty fun!

Go Buzz Lightyear!
To make the moon rock for this design, you can use a sponge. Cut it to shape and use white acrylic paint to paint it. The effect really does turn out like moon rock.
The background is blue acrylic paint with white dots to look like stars. Some planet stickers help create the look of space even more!
Buzz light year is a resin figure found at the dollar store while the To Infinity and Beyond and Buzz on front are both paper cutouts. 

  It's nice when you find a TinkerBell figure at a thrift store and know you can use her in a night light project!
The background is a painted acrylic forest, and a cut out of a treehouse is behind her. Some craft grass was used to look like a forest floor. Everything hot glued in place.\
The TinkerBell sign is paper and the fabric flower matches the blue sparkle paper on the bottom as well as the cute dragonfly in the corner.
Its' all about creating the perfect color theme for your design.

Painted plastic zombies, Daryl and Rick, the Walking Dead!

A friend requested a TMNT night light for his grandson

A circus style mermaid night light.

 

The Little Mermaid, this nightlight totally looks like she's underwater.

Frozen night light.