ScrewYourMobs!

!Stylized creeper with a red, circled strikethrough above it, indicating it's demise. Minecraft-font text next to it reading "ScrewYourMobs!"

Previously known as "Screw_SubAnomaly1".

Automatically despawns entities the moment they spawn! Based on JSON rules you write yourself.

Originally built to remove TheBrokenScript's SubAnomaly1, now a general-purpose entity filter!

Features

Rule-based removal. Each rule is a JSON file listing entities and the dimensions it applies to. Entities are discarded the instant they join the world.

Entities or tags. List specific entities (minecraft:creeper), entity tags (#minecraft:raiders), or both in the same rule.

Per-dimension or global. Leave dimensions empty and the rule applies everywhere. Fill it in and it only fires in those dimensions.

Drop-in rule files. Rules live in config/sym/rules/ (global) or <world>/serverconfig/sym_rules/ (per-world). Edit the JSON, run /sym reload, done. No restart.

In-game rule editor. /sym, /symrules open a GUI. Add, remove, rename, enable, disable, and validate rules without touching the filesystem.

Live validation. On load, entity IDs, tags, and dimensions are checked against the registry. Unknown entries get flagged with a "did you mean…?" suggestion based on edit distance (Levenshtein). Missing mod namespaces are reported separately.

Keep list. Exempt specific entities from removal entirely, regardless of what any rule says. Also skips named mobs and tamed animals during bulk purge.

Server-side sync. On multiplayer, rules are synced from server to client so the editor shows the real state. Edits are permission-gated (op level 2) and round-trip through the server.

Debug channels. Optional logging for removals, rule errors, validation, and reloads. Output goes to console, chat, and/or config/sym/debug.log, each toggled independently.

!Image showing the in-game rules editor

Commands

All require op level 2.

Command	What it does
/sym	Open the rule editor (singleplayer / LAN only)
/symrules	Client-side alias for the editor (used for dedicated servers)
/sym list	List loaded rules
/sym reload	Re-read rule files and re-sync to clients
/sym stats	Rule and entity counts
/sym validate	Show validation warnings
/sym debug	Show or set debug channel state

Requirements

• NeoForge for Minecraft 1.21.1, at least version 21.1.100

Example rule (also available in config/sym/rules/_example.json)

{
  "_comment": "Copy this file and rename it. Delete the _comment fields if you want to.",
  "_comment2": "Empty 'dimensions' list means the rule applies in ALL dimensions.",
  "_comment3": "Tags like '#minecraft:raiders' are also supported.",
  "entities": [
    "minecraft:creeper",
    "minecraft:skeleton",
    "#minecraft:raiders"
  ],
  "dimensions": [
    "minecraft:overworld"
  ]
}

An empty dimensions list means the rule applies in every dimension. Rename the file to start with _ to disable a rule.