Creepers are a kind of fungus. Yes, Creepers are mushrooms that explode...which is not entirely odd when you think of how some mushrooms spread their spores. The exploding is their reproduction phase, they swell and then BOOM spores are dispersed just like stepping on a puffball.
Why do they chase after me then? Because you are in their territory and therefore a threat to their environment. If they were hunting you as food or going to use your dead body as a place to plant their spores then they wouldn't blow you into a million tiny pixels. Think about it, a mushroom that size (approximately 2 meters tall) must have a MASSIVE Mycelia colony stretching underground. And there you are tunneling and digging and disturbing their Hyphae so it makes sense that colony would send its fruiting stage out to chase you off and to spore at the same time.
How do you harvest the gunpowder then? Well Saltpeter is found in caved thanks to bat guano, Fungi needs sulfur for metabolic processes, and there is a ton of coal from all those fossilized trees...most likely they store it for their explosive sporing and if you kill them without their sporing you get some fancy gunpowder.
Ben thinks their face is just an interesting pattern to intimidate things to keep them away and not actually a functioning face, that they use sound or vibrations to find things in their territory. I think it is a face and they can see me...and that they are malicious...
|That is under my front door|