Yeah can't think of any tricks in GG to accomplish a portal type game. Really need a second camera and a way to render that onto the portal. It could be done in AGK I think, but as AGK is what I think of as a proper programming language, the extra options make it extra hard to do everything.
It's amazing how everyone wants to make a clone of a top seller as their FIRST game. Well, not that amazing, but seriously, try to think smaller, making games is difficult, even in GG. Back in the day us more mature members had such game making tools as Pazzaz, which I wasted a good chunk of cash on back then. Rubbish, but let us know in no uncertain terms that we had to learn to code to have any chance at all, lol.
The Speccy one was even worse.
SPECS: Ryzen 1700 CPU. Nvidia 970GTX. 16 Gig Memory. Win 10.