What do you think about DXX-Rebirth

[Descender1032]

It's been a while since I checked this, but my recollection is that if you escape to a secret level while the countdown is running in the main level, you can't go back to the main level.  Hence, if you put the secret level teleporter behind a reactor-triggered door, you guarantee that the player won't use it until after the countdown is running, so you guarantee that the player must advance to the next regular level.

That's correct. But still, if you die once in the secret level, you still get sent to the next one, unlike D1 secret levels, which you can attempt as many times as necessary, just like any regular level.