How do I make a player die when they step off a certain block?
In order to do this use the following
/execute@e[type=player] ~~~ detect ~~~ minecraft:stone 0 kill@e[type=player]
the detect will see if a(n) entity steps on a certain block. IF the entity is on that block then the command will execute. Any other block you want them to die on then set up a chain command block