"Creepers" are mobs made from coding bugs. They are kinda disguised like tree leaves, two blocks tall, and you hear a hissing sound before they blow up like TNT. They appear at night, and don't burn in the daylight, so you either have to kill them or wait until they despawn.
There aren't "ancient creepers" in the application version of Minecraft, there are creepers.
It's called Minecraft... creepers have ALWAYS been in Minecraft.
No, Creepers just flee from them.
Yes, creepers were an error, they messed up a pig...
Yes
No hostile mobs (including creepers) are present in peaceful difficulty.
Monster spawners do not (as of the version 1.3.1) ever contain creepers naturally. It is possible to get a spawner that spawns creepers by editing the game's code or by using mods.
Yes
Kill Creepers.
Yes
They explode once they sees you.
Yes, they will explode.