The Tunnel Entity

Hello, you can call me Tyson, and what I will tell is one of the not only strangest things, but one of the creepiest I have seen on Minecraft.
=== Context ===
I have played Minecraft since 2017, and in all my years of experience, I have made a lot of tunnels, a lot. 
But none of these was like the tunnel I and my friend made in our semi-anarchic world
Well, in the server we're only 3 people, one of them we'll call him shadow, and the other one ztax. Yesterday ztax broke one of the only rules in the server, do not tamper with the snow biome, which is shadow's territory, so when ztax disconnected, I and shadow decided that we could kidnap one of his villagers as a revenge.
=== The plan ===
The plan was simple, get his most valuable villager and put it on a boat, then, create a tunnel from ztax village, to another village which is property of shadow, we started with the plan, the villager got in the boat and we moved the boat to a nearby mountain to start making the tunnel.
=== The tunnel ===
We started to make the tunnel, it was a straight line from point A to point B, quite the easy task, well, you know that uneasy sensation that someone is behind you? Well, that's how it felt, me and my friend took roles, at the start he moved the boat and I made the tunnel as well as I placed the torches, when my pickaxe broke, he was the one making the tunnel, and I moved the boat as well as I placed torches, well, at some point, looking behind you and seeing the whole tunnel was terrifying already, even when there was nothing, until, my friend told me to NOT look behind... At first I was confused, and my sense of curiosity was bigger than the sense of reason, well, what I saw behind, between the unloaded chunks, some weird black tentacles, it was scary, but obviously it was a bug with the chunks trying to load or something, so we kept going, tho, when my friend looked behind again, there weren't black tentacles... But a figure, he described it like an Enderman as tall as a player, this time I did not look behind, we started rushing to get to the other side, now, my curiosity took control over me again, and when I looked behind, the only thing I saw was something like a head coming from one of the holes we made to mine iron earlier, this time I told him to rush, we didn't care about putting the torches correctly anymore, we were just running and mining, at some point, the thing behind us changed colors, now it was a brighter color, we did not care, once we finally mined out of the tunnel, we blocked the exit, as the entrance was already blocked by my friend, the creature was trapped in the tunnel... Or so we thought.
=== After the tunnel ===
When we got out of the tunnel with a villager, two mini zombies appeared and not only they killed me, they also killed the villager, all our progress was lost, we refused to kidnap another villager, and even less, we didn't want to go back to the tunnel, so we both logged off, and in the exact same time I logged off, my Nintendo switch just turned on, I didn't press any button, I didn't do anything, and the nintendo switch only turned on, my friend decided to go back to the world, and the first thing he saw while the chunks were loading, was a black figure with tentacles in his back, the tentacles weren't the ones from a squid, the tentacles were twisted, and one of the arms of the creature was like a tool (like an axe or a pickaxe) when my friend's chunks loaded he went to where he saw the creature, behind a mountain, and when he arrived, there was nothing, and not only that, night was slower and day was faster, for example, daytime now lasted about five minutes or so, and night occupied the rest of the day, after that, I refuse to go back to that minecraft world.
I got no footage, the only thing you can trust is my word.
(The 95% of this story is based off of real events)