Thanks! I used the textures supplied by Epic Games for the materials (but only used as diffuse maps trying to get the game as small as possible for HTML5).
I did struggle trying to design a way for the player to understand what to do (without using text) - my solution was to place the player directly pointed at the one plastic cup, and hoping the player accidentally shot the cup when starting the level. Looking back, I could have put a "target" around each of the green mermaid images, or set up a ball that falls onto a cup while the player is looking, in order to teach the player that they can be shot?
Thanks for playing!