Cool. I was hoping that people's knowledge of building Mario Maker levels, they would subconsciously not panic and think they're in the same room and make it ridiculously hard on themselves... The Thwomp is supposed to be more of a surprise than a real puzzle solution.
When I was playing around with it, I discovered that you can have a pipe entrance and exit lead to the same place if you stack them. You could have Room A that connects to Room B, which is a dead-end. And then you can have the player go back into the Room B pipe to exit and end up in Room C. If there are two entrance/exit pipes on top of each other, the game will use the one you created first as the one that is active. So if you created the Room C <- Room B connection and then made the Room B <- Room A, it would flow A -> B and they can't get back to A, that B pipe leads to C. It's really finicky and annoying, though.