DISCLAIMER: I am not the owner of the mod. Made by PFKL, videos by @LookOut3D.
This mod can grief your world, contains jumpscares and loud noises, and can disable your cheats. Make sure you use the Moderner Beta world type.
If you have trouble with Essential not working, disable Nostalgic Tweaks ("O" key -> config -> Mod enabled/disabled option)

Lore:
You found this old world laying here, in your files. Very old, huh? You take a look. You run Minecraft, add the world in the folder, and play. Surprisingly, it's empty. Nothing in your inventory, no levels, no armor. You wander around, and you find structures you don't seem to remember buidling. How are they here? You didn't play on this world.
Time passes as it should. But something is wrong. Then you see it. A horse, staring at you from a distance. It's not the vanilla horse. It's white, dirty, distorted. It doesn't appear to move. As you get closer, he whispers to you... saddle him. Saddle him. You must saddle it.

Saddle it. Brush it. addle it, brush away the flies, feed it, hide from it, and survive its hunts. When a task is complete, the world turns into a new stage, while failure causes the horse to become faster, more aggressive, and capable of tearing through blocks to reach you.

He watches from a distance, appears without warning, reacts to nearby players, and remembers when someone cheats. Using commands, Creative Mode, illegally obtained saddles, or trapping the creature may trigger additional penalties, shorter timers, revoked commands, and new tasks.

I do not own the models or the mod. Keep in mind this is a modpack.

LookOut3D's horse.jar