You could try using Backbone, it's easier to use than Shockwave. Backbone is available on Aminet, along with an update and a recently released keyfile to unlock the full program without limitations!

All you need is a mouse to make games with Backbone. Just download some sprite rips and mods from the net, change them around, and make a game out of it!

There are some good royalty-free characters to use like Santa Claus, Christmas Elves, Snowmen, or just a kid in winter clothes. Collectables could be presents, toys, candy canes, tree decorations, roast turkeys. If you want to be a smarty pants and give Santa a machine gun and have him riding an angry mutant reindeer feel free, be creative.

You could also use Shoot Em Up Construction Kit, or an adventure game maker!