I want to make a map with some commands, one being when the player gets within ten blocks of a command block, a door is revealed or a boss is summoned. I couldn't figure out how to do it. Can someone please help? Thanks. I might have figured out the problem.
You can do that in one command block:
Put a comparator next to it with the input side facing the comparator, and then you have to trigger that command block all the time.
When there is a player within a radius of 10 (10 from each side) the comparator gets activated. Then you can make that redstone signal do anything.