Oh really? The assets aren't actually 3D in-engine, they're pre-rendered sprites. I'm unsure why the game was lagging. What machine are you running? My testing was all on high-end computers.

it works. 
i just tried it, did you bring it back to the box at the beginning of the level?

I tried walking outside the map, and I was able to do it, so maybe you can add some invisible walls to prevent the player to do so. (If there are walls already, check their locations).

I think, just that... I didn't encounter other bugs / glitches.