Rebirth of the Mobs
is an extraordinarily customizable framework intended to allow modpack and adventure map creators to customize entities' combat potential. It has all sorts of applications, from "making all players immune to fall damage" to "Make husks explode into a swarm of silverfish on death" to "Cause the Ender Dragon to summon Shulkers to defend itself". ROTM is compatible with all modded entities and potion effects.
Unconfigured, ROTM will have minimal impact on your game.To get the most out of this mod, you'll need to understand each configuration section and customize them to your liking. Remember - "minecraft:player" counts as an entity, too!
Damage Sources
In this section, you can configure entities to be immune to specified damage sources. Vanilla damage sources include "cactus" for cactus damage, "mob" for generic entity damage, "player" for player attacks, "arrow" for arrows, "inWall" for suffocation, and "fall" for falling damage, among many others.
Optionally, the type of damage can be set to be entity specific: for example, "minecraft:zombie;minecraft:skeleton;arrow" will set zombies to be immune to arrows fired by skeletons, but zombies will still take damage from arrows fired by dispensers, players, and illusioners.
Cancel Potion Effects
Are you sick and tired of the Nausea effect? Do you want all monsters to be immune to wither? In this section, you can configure entities to be immune to specified potion effects.
Death Spawns
We all know monsters from video games that unleash other monsters when they die. With the Death Spawn feature, you can recreate that trope to your heart's desire. If you want the Wither to seemingly "transform" into a rabbit on death, that's possible. If you want the Gaia Guardian from Botania to erupt into every insect from the Erebus when killed, that's possible too. Spawned entities have support for NBT tags.
Instant Health Regain
Most games with bosses have those bosses reset back to normal if you fail to kill them. Not Minecraft. Isn't it a shame how lazy "grave rush" strategies are viable for even the toughest modded monsters? Not anymore! In this section, you can configure specific entities to regain a percentage of their health whenever a given entity dies nearby. This isn't just useful for bosses, either: you can use this to make it so wolves regain health whenever they kill sheep, or the player regains a portion of their health whenever they kill any creature. The field "Last Man Standing" determines whether this feature activates on a per-kill basis. With Last Man Standing set to "true", you can allow boss strategies like in Terraria where one desperate player can fend off the boss long enough for the rest of the squad to respawn and get back into the fight. With the feature set to "false", any specified entity dying within the radius will heal the main entity by the percentage you specified.
Mob Defense
A lich with an aura of fiery retribution; a slime with acidic blood; an evoker cursing archers with blindness. All of these features and more are possible with "Mob Defense". In this section, you can specify mobs to apply potion effects to their attackers. You can optionally specify a specific damage source to trigger the effect: you'll want two lines for "mob" and "player" if you just want the effect to be triggered by melee attacks.
Mob Offense
Husks inflict hunger; Strays inflict slowness; Shulkers make you levitate. But what if every mob could cause a status effect? Mob Offense can make that happen. This feature was inspired by mods like Rough Mobs, which by default include all sorts of features such as spiders inflicting slowness, Endermen inflicting blindness, and zombies inflicting hunger. Mob Offense takes that to the next level by offering you complete control over both the monsters and the statuses they might inflict.
Summon Spawn
Have you ever looked at an Evoker and wished that other monsters could summon minions? Wish no more. An extraordinarily useful tool for creating custom boss fights, the Summon Spawn feature can allow any entity to call in the cavalry. Options per entity to enable or disable XP and drops from the summoned minions ensure you don't accidentally turn your custom boss into a cheesy source of infinite loot. Spawned entities have support for NBT tags.
Vehicle Configuration
The definition of "boat" is a small vessel propelled on water by oars, sails, or an engine. There's nothing there about "a viable deathtrap for any and all enemies small enough to get stuck". If you're bothered by players using boats to trap monsters, are sick of sheep falling into your chest minecart-based item sorter, or don't want a specific NPC in your world to be able to be shoved into a wagon and hauled across the continent, Vehicle Configuration offers complete control over which entities can mount what entities. In general, this is intended for use with vehicle entities, but you could absolutely use this to prevent players from riding pigs or horses, or disabling spider jockeys once and for all.
Miscellaneous Configuration
Several assorted features. Global Swim Speed Multiplier lets you scale the swimming speed of all entities, allowing you to make every swimming entity the equivalent of a lead weight, or Michael Phelps, or all the best parts of Sonic the Hedgehog and Jesus. Its associated blocklist lets you exclude entities from the universal scaling, or turn the whole thing into an allowlist instead. Natural Spawn Buff removes the silly limitation of transparent or half-blocks preventing mob spawns, allowing monsters to spawn on leaves, slabs, glass, and everything in between.
Debug Configuration
This mod is not easy to use without knowledge of internal names for entities, potion effects, and damage sources. While some other mods might offer ways to view all of these names at once through dumps to .txt files, ROTM nonetheless includes an optional debug mode to grab the names of all of these things per-entity. Especially useful is the Damage Source Debug, which lets you right-click an entity to figure out the last type of damage it was affected by. Without peeking into individual mods' actual code, it would otherwise be very difficult to determine whether some modded mobs might use "magic", "indirectMagic", or "mob" for their specific attacks.