Hello, I've been working in game maker, but I've been wondering if there's a way to import a game maker file into unity without re-writing the whole game or open up a game maker game from inside a unity game?
No, that won't work, but you can reuse your sprites from Game Maker. If you have Game Maker 8.1 Pro or any version (including the free one)* of Game Maker Studio you can export your sprites to image files and import those to Unity. Unity and Game Maker work in very different ways but Unity is pretty cool and powerful. *As far as I know, might be wrong but I think even the free version of Studio can export sprites.