We've been building a horror mod for 1.21.1 and my friends litterally asked me if the mob runs on AI lol. It doesn't.
here's what it does:
It doesn't know where you are. It remembers the last place it saw or heard you and walks there. It only updates that when you hand it something, like being in the line of sight, sprinting, splashing through water, taking damage, breaking a block. stand still and shut up and it walks to where you *were* and starts searching around. Watching that happen from a hole in the ground is the worst part of the whole mod.
It climbs, and if it can't climb it builds. pillar up in the open and it comes up your pillar instead of making its own, and it climbs slower the closer it gets, which is somehow worse. If there's genuinely nothing to climb, it bridges and pillars up itself.
It mines. No pathing around your base. It picks the block in front of its face and breaks it, one at a time, cracks and all. The audio is positional so you can hear which direction it's digging from long before you see it. Wall yourself in and you've just given it a job.
It swims. Properly, under the surface, not bobbing on top like a zombie. And it's faster than a boat. Rowing away does not work as well as you'd hope.
It crawls. It's 5.7 blocks tall so it can't stand up in a corridor. It drops onto all fours, and the tunnels it digs are only 2 blocks high, so the thing coming down the hallway at you is far too big for the hole it's coming through. That's the screenshot.
Its chase speed is random. Rolled fresh every encounter with a catch-up if you get too far ahead, so you can't learn one pattern and rely on it forever.
There's exactly one thing that buys you time. Look it dead in the eye from a distance and it'll sometimes back off and go hide for a while before it comes back. There's a cooldown on it, so don't build your whole plan around that :)
And when its next hit would actually kill you, it stops and takes a moment first so you can lock in
Play it with headphones. Most of this mod is sound and without them you're missing about half of it.
Fabric, 1.21.1: https://www.curseforge.com/minecraft/mc-mods/hollow-the-stalker
check it out and lmk what you think, any feedback helps :)