RZero

RZero: Return by Death

RZero is a survival mod that replaces the standard death and respawn mechanics with a timeline rollback. Upon death, the world state is reverted to a previously saved checkpoint.

How it works

The mod records the state of loaded parts of the world, entities, and players. When a rollback is triggered, either upon death or manually, the game engine rewinds time back. To ensure consistency, the mod modifies the internal logic of the random number generator. This means that if you perform the exact same actions after a rollback, random events, such as mob spawn coordinates or item drops, will trigger the same way as in the original timeline.

What is subject to rollback

The rollback affects various aspects of the loaded world:

• Blocks: Blocks placed, broken, or destroyed, for example, from a TNT or creeper explosion, after the checkpoint are returned to their original state.
• Entities and mobs: Monsters and animals are returned to their previous positions with their previous health values. The mod restores their AI state, including current targets, pathfinding routes, and memory modules, such as villager trade states or piglin aggression.
• Players: Inventory, health, hunger, experience, potion effects, and item cooldowns are restored.
• World state: Time of day, weather, scoreboard values, and active raids are returned to the state at the moment the checkpoint was created.

Multiplayer: Anchor System

RZero operates on a global scale. It does not create separate timelines for each individual player.

• Anchor: Each checkpoint is tied to an "Anchor" player, which is the world creator or server host.
• Global rollback: If the anchor player dies, the entire world rolls back to the checkpoint. The positions, inventories, and states of all other online players will also return to the moment when the save point was created.
• Offline players: If a player leaves the server after a checkpoint is created, and the server rolls back while they are offline, the mod makes changes to their saved .dat files. Upon the next login to the game, they will be in a state corresponding to the rolled-back timeline.

Auto-saving systems

The mod includes different background saving modes that can be toggled via gamerules:

• Interval Mode: Creates checkpoints based on a timer. This can be a fixed interval or a random time period between specified values.
• Director Mode: Evaluates the current threat level and creates a checkpoint only in a calm moment after the danger subsides.
• Safety Veto: Blocks the creation of checkpoints in situations of inevitable death, such as burning in lava or falling into the void.

Usage, commands, and configuration

The mod works automatically, but it can be configured using gamerules or commands, which require enabled cheats or administrator rights.

Commands:

• /rzero set — Manually create a checkpoint at your current position.

Hotkeys:
Keys for manual saving and manual rollback can be assigned in the Minecraft controls menu.

Main gamerules:

• rzeroAutoSave — Enables/disables the automatic checkpoint system.
• rzeroFixedInterval — Sets the fixed time between saves in seconds.
• rzeroUseDirectorMode — Toggles the Smart Save heuristic system, also known as Director Mode.
• rzeroDirectorInterval — The minimum calm time required before saving in Director Mode.
• rzeroPlayRollbackSound — Enables/disables the sound effect during time rewind.