Mobility

Walls are a suggestion. So is height, and so is distance.

Mobs dig through whatever is between you and them. They stack blocks to climb to you and bridge gaps to cross to you. They swim, open doors, walk through fire, and when they finally lose you they go and search where you were. They see you through blocks. And they arrive in real armour, with real weapons, some of it enchanted, and some of them carrying bows they have no business knowing how to use.

For Minecraft 26.2 (Fabric).

Installing

1. Install Fabric Loader for Minecraft 26.2.
2. Put mobility-1.0.0.jar and Fabric API in your mods folder:
   • Windows: %appdata%\.minecraft\mods
   • macOS: ~/Library/Application Support/minecraft/mods
   • Linux: ~/.minecraft/mods

Only the server needs it. Vanilla clients can connect and play normally.

Works on an existing world. Mobs that are already alive get the digging and the eyesight immediately; the armour and weapons only appear on mobs that spawn from now on.

Digging

A mob looks along the line between its eyes and yours. If the first thing it meets is a block rather than you, it starts chewing through it, with the same cracking animation a player's mining makes.

Nothing decides in the abstract that a wall is "in the way". If the mob can walk around, its pathfinding takes it around, the line clears itself, and the digging stops. It only digs when digging is genuinely the shortest way to you.

It also checks at knee height as well as at eye height, so a mob whose head clears a wall but whose legs do not will still dig its way out.

Hardness matters. Dirt goes fast, stone goes slowly, and the mob has to stand there and work at it. You can hear it coming.

Some things are safe. Bedrock and anything else unbreakable, obsidian, crying obsidian, respawn anchors, reinforced deepslate, ancient debris, netherite blocks and enchanting tables are never dug. Chests, furnaces and spawners are left alone too by default, so your storage room survives.

/gamerule mobGriefing false stops it, along with everything else that breaks blocks.

Pursuit

This is the part that makes them feel intelligent rather than merely violent.

They do not give up when the path runs out. A vanilla mob asks the pathfinder for a route and, if there is not one, stands there. These keep coming: the mob is pushed bodily at you, which presses it against whatever is in the way and hands the digging and building goals something to work on.

They swim. Water is a road rather than a wall, and they float instead of sinking.

They open doors -- every mob, not just zombies on hard -- and treat a closed door as a route rather than a dead end. An iron door they cannot open, so they dig it.

They walk through fire and other things that hurt, if that is the shorter way. Not lava. Lava is not determination, it is suicide, and a dead mob has stopped hunting you.

They remember. Break line of sight and get away, and the mob walks to the last place it saw you and searches from there for fifteen seconds. Losing a mob now takes distance, not a corner.

None of this runs while ordinary walking is still working. As long as a real path to you exists the mob is left completely alone and behaves like any other mob -- which is what stops all of it from fighting the vanilla AI instead of helping it.

Building

Digging only ever gets a mob through something. This is what gets one up.

If you are above it with no way round, a mob starts stacking blocks under its own feet and riding them towards you -- the same jump-and-place trick a player uses. Because it is done that way rather than by teleporting blocks into place, it obeys the same rules you do: it needs headroom, it cannot build through a ceiling, and it gets stuck on exactly the things that would stop you. If there is a ceiling in the way, the digging goal takes it out and the tower carries on.

If the gap is sideways instead of upwards, it bridges: laying a floor block ahead of itself and walking out across it.

The towers do not last. Every block a mob places is remembered and taken back after ninety seconds, so a long night does not leave the landscape covered in dirt pillars. Nothing standing on a block is ever dropped -- if you are on it, it stays until you are not.

A pillar of dirt appearing outside your window at 2am, one block at a time, is the intended experience.

Eyesight

Mobs see you through walls. Their range is unchanged — they still have to be as close as a mob normally would — but a stone wall no longer hides you inside that range.

This is the difference between this mod and Big Brother: this is a mob noticing you are on the other side of a wall from ten blocks away. That is every mob in the world knowing where you are from any distance at all.

Equipment

A mob rolls for gear once, when it spawns, and keeps whatever it got.

Armour comes in full sets, from leather up through gold, chainmail, iron and diamond. Which set it rolls leans on local difficulty — the same number vanilla already uses, which accounts for how long the world has existed, how long you have been in the area, and the moon. Early game stays survivable. A long-lived world does not.

Weapons run from a wooden sword up to a diamond axe on the same scale.

Some of it is enchanted, with the enchantment strength scaling the same way.

Bows go to things that should not have them. A quarter of the mobs that would otherwise get a melee weapon are handed a bow instead, and a goal to go with it that any mob can use. A zombie with a bow shoots you at range and keeps shambling towards you between shots, because the archery does not replace its normal behaviour, it runs alongside it.

Drop chance is low on purpose — about 4%, half the vanilla rate. Mobs are being handed far more gear than usual, and without this the floor would be knee deep in iron boots.

Effects

Roughly one mob in six spawns with a potion effect that lasts its whole life: speed, strength, resistance, fire resistance, regeneration or invisibility. At higher local difficulty the effect can be level II.

An invisible, enchanted, diamond-armoured skeleton is a possible thing to meet. Sorry.

Commands

Settings

A file appears at config/mobility.json the first time you run the mod. The parts are independent, so you can have the digging without the diamond armour, or the reverse.

Things worth knowing

• A roof is no longer enough. It was, when all they could do was dig sideways. Now they climb.
• Torches and light are still your friends. None of this makes mobs spawn where they could not spawn before. Lighting your base up still works, and is now considerably more important.
• Obsidian is a real building material now. It is on the never-dig list for a reason.
• You can hear digging. The cracking animation and the sound are your warning that something is coming through a wall.
• The improvised bow keeps its distance sensibly. A mob will not shoot you point blank; inside four blocks it goes back to hitting you.
• This pairs viciously with Big Brother. One lets mobs see you through walls from ten blocks away, the other from anywhere the server is simulating. Together they will find you, walk to you, and build a staircase if they have to.
• If the dirt towers bother you, drop scaffoldDecaySeconds to 30. If you want the ruins left standing as a monument, set it to 0.