I went over to my friends house one day. We went onto her Xbox and created a new Peaceful Survival game. We made a house, everything seemed normal. We are obsessed with finding Herobrine, so our quest was to basically find him. We had left a cake outside and a sign saying "Herobrine, come and fight me like a MOB". We went mining, we couldn't find him. So we found a ravine, and when we were about to jump in, something hit me from behind and I fell in and died. It was really weird, cause my friend didn't hit me. After that, we went back to the house. The cake was gone. There were no other players in our game, just my friend and I. We didn't think too much of it though. I went to the desert to get sand (to make Glass for our house) when I saw a player in the distance. My friend was at the house though, and nobody else was in the game. After that, I showed my friend, and we basically freaked out. We then deleted the world.
It was weird. Was it Herobrine? I'm still not sure.
Note: There was no mods or hacks installed into the game at that time. All of this is true.