I am working on a late entry, inspired by my daughter's request to create a video game for her.
The working title is "Mermaid". The objective is to collect treasure and locate the queen's crown along with the key to the underwater castle while avoiding various sea creatures including the shark, octopus, squid and a variety of fish.
The mermaid can protect herself with a "mermaid bubble" (force field) and also has a "speed boost" option to briefly increase her swimming speed.
Once you collect the key and the crown, locate and enter the castle. You need to deliver the crown to the queen before time expires.
Here are several screenshots.