Okay, so my idea for this consists of the following:

You’re a big entity in a small world. You’re too big for certain corridors. You’re a big man in a Tiny World.

However, some kind ‘thing’ has given you shrink pads around the place! Yay!

Great! So we can fit in tight places! (Innuendo somewhat intended), but there’s a catch… as always.

You can only be shrunk for a certain amount of time.

That means, if you’re in a small corridor when your time is up;

You will die.

Anyway, there are various other elements to add yet, but I’m making nice headway.