@Marina Agreed. Anything past the first one was a waste of time other than to see creative way of hurting/killing someone. Plus, one year between films isn’t really good. Makes them all seem rushed.
To answer the question, (from the first film) being alone in the bathroom, in the dark until death via starvation, thirst, or means of suicide. At least the other methods were…well, not fast, but somewhat faster then slowly dying, being alone, and going insane in there.