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
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
two libraries on the same stronghold
look at how many cobwebs this library has!
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.