Enirbyon

My name is Enir. Back in July 2011, I started a new singleplayer world in the Minecraft Beta version. Everything started out rather normally, as I began to progress in the game, getting wood for tools, and then quickly upgrading to stone as I knew how to do. Sometime during the playthrough, I started getting the tendency to build random markers in the world to mark places I've been, or if I get the idea for a funny little building, I'll put it there. Even just things like torches to mark where I've been (something I'm sure a lot of people do in their worlds). The weird occurrences began when I came across a pit in the ground I dug before, except that now it had a ladder going down into it, and a torch at the bottom. My friend Giovan had a server around that time where we met up, and so I hopped on to ask him about this strange occurrence, but he said he didn't know anything about it. 
As I continued on the world, the strange occurrences became more and more frequent. Random blocks missing from trees, random saplings placed in forests. Eventually, I encountered a strange starter house with nothing in it but a bed, a crafting table, and a chest full of random early loot, mainly, wood. There couldn't have been anyone who built it, so I just took the loot and moved on. However, as I left, I saw a strange figure off in the distance. It wasn't another person, because this was a single player world, but its name was "barusa_miko123". I turned around to get a better look at them, but I couldn't spot them (though I could swear I saw them peeking out from behind a tree once during that). I continued heading back to my base, noticing along the way that one of the little sand pillars I had built to help me find my way had had a couple of its blocks removed, and another pillar made out of stone was built next to it, and several of my torches had been removed, leaving only the cobblestone blocks they were on. Not only that, but there were torches placed that I definitely didn't build (they were on 2-block-tall wood towers, rather than 1 block of cobblestone). I noted down the location of that house and decided to work on getting better equipment myself. 
The next day, I decided to head back to the house to see what was up, and along the way I noticed random tunnels in mountains, as well as random staircases down to nowhere, sometimes leading to caves, which would be sparsely lit up. Presumably by Barusa Miko or whoever? 
Once I arrived at the house, it seemed to have been expanded sort of like mine, with an extra storage room and more advanced loot. However, as I was poking around, Barusa came up and attacked me with a diamond sword. I turned around and faced Barusa. Barusa was a half-Steve half-creeper, and we started fighting, though Barusa seemed to be very good at combat and killed me. I had a lot of my precious loot on me - my iron tools and single diamond included. After respawning back at my base, I left the world to go chat with Giovan some more. Giovan was even more confused than before, some supposed being in my world that was building weird things and came and killed me, he didn't know anything about it! I just decided to go to a new world that hopefully didn't have Barusa or whatever in it, and that's still my main world to this day.
Hello.
My name is Enirbyon3. You can call me "Enir". I am a codeling. Or, a class-H entity. That is, I exist within the world of Minecraft itself. Barusa Miko is a player, someone who exists outside of Minecraft but is experiencing it as a game - it just so happened that at that time in my life, I was completely unaware of players as a concept. Barusa was just normally progressing in her world, building a house, mining, leaving torch markers, checking out weird things. When I stole her stuff, she understandably got mad at me. It seems that instead of starting a new world as I had planned, I had accidentally visited her world.