The Web's Dear Freja

My favorite APL thing is being able to change whether arrays are 0- or 1-indexed during execution of a program. I assume it's more or less exclusively used once at the start because a programmer has a strong preference, but the idea of changing it in the middle of a program, maybe even multiple times, is so funny to me, as someone who loves chaos and psychic damage and death. Possibly one of the worst features you could have in a language? Just great stuff.