@silverwizard Hard isn't bad. But D&D does offer a lot of the tools of what I want. Plenty of systems don't have half of this stuff.

mobility is pretty bad in D&D - the Dragon can move real fast
Also an issue I've been thinking about. If he's losing, can't the dragon just fly away?

There's a lot of like, web, dimensional anchor, and other tools to make it slow down.
Web is an interesting idea. Though wouldn't the Web be too small to capture an entire dragon? And wouldn't the dragon be too strong and easily break loose? But it's exactly the sort of thing that, if they try it at the right time, will probably work.