I used to have the same issue and whenever I increased the memory it said I was exceeding java limits, so I couldn't increase the memory but I couldn't decrease it also, because it said it needed more (and whenever I added more it said I exceeded).
These are pictures of intersting and weird things I found on your seed
[media]
A forest fire (which is relatively common) but instead of breaking leaves, the sound were of breaking wool
a lonely pumpkin
weird lava corridors
amazing cave formation, a completely closed room filled with water heated up with magma from the lava underneath!
drowned walking underwater and acting like a zombie
[media]
two libraries on the same stronghold
look at how many cobwebs this library has!
[media]
an absolutely MASSIVE (more then 5000 blocks wide) taiga biome over the stronghold
Hey Sun Ruizheng.
I have had some cases simlar to yours! I always knew anything like another player in your single player world is impossible but I still can't understand what happened to me 5 years ago. I was playing Minecraft PE and I had a survival world in which I played in for a very long time, there, I was playing. I was exiting my house to explore when I was exploded by a creeper. I spawned again, grabbed my stuff back and when I was exiting my house again I was again exploded, but this time, the explosion was a LOT bigger and half a second before I died I swear I could see Herobrine hiding behind a tree in front of me. I exited the world immediately and deleted it. Since then Minecraft never worked anymore on that iPad. I think this case was actually a trick my brain played on me, but this next one I really am 100% sure it was real: It happened on https://classic.minecraft.net/ one month ago. Basically I was alone in a world after hearing about how multiplayer was closed on this website, so even if I shared my link with someone (which I didn't) they wouldn't be able to enter my game. I was digging out of a hole when I saw a Steve coming up to me, I got shocked and he disappeared (I had my render distance on tiny to reduce lag) when I ran /list he had gone already!
Awesome! This feels so sneaky!
I sometimes have the same issues when my game is lagging to much or is about to crash.