Scratch

That is a very broad request. Do you have any of this scripted yet? If so, please post it and add a link. I'm not sure how much experience you have with Scratch or programing in general but if it is not a lot yet, you may want to start with something easier. But if you get something started and upload it, you will have better responses here in the forum. At least get the sprites you want in the game, upload it, and then ask again.

Better yet, find someone else's game that has similar functions to what you want, download their script and see how they do it.

In any regards, here is a quick answer that will probably be little help, sorry. Find the sprites you want to use, or draw them yourself. Anything that moves will need multiple animation images loaded as sprite costumes in order to look "right" in the game. You will have to decide 1) how the dragon is attacking the princess and what stops or doesn't stop it from hitting her 2) what the prince is shooting at the dragon 2) extra sprites faded 100% invisible to be used as collision detectors behind the arrows/flames/prince/princess/dragon/etc 3) use multiple variables to keep up with damage, etc 4) much more!!

If you are somewhat new to Scratch, I recommend going this route... sketch out with pencil and paper a rough idea of what you want the game screen to look like. On your computer, draw up a background and add that to the stage. Then add your prince sprite. Will it have a side-view? Does the prince only walk left and right? If so, work on making him walk back and forth. That would be a good start and would show people that you have put time and effort into your project. Upload it and you will get more/better responses on continuing to add more features. There is a ton of Scratch resources and how-to information both here in the forums and at the main Scratch site. You just have to do some digging. Peace.