Enemy Aggro

Enemy aggro refers to the behavior and mechanics around how certain enemies come to notice and attack Link. These mechanics are surprisingly robust and influence the way speedrunners approach certain enemy encounters.

Basic mechanics

Broadly speaking, enemies fall into a few different AI patterns:

• Unreactive enemies. These are enemies whose AI ignores Link entirely. Examples include baris (jellyfish), pokeys, mini-moldorms, rats/crickets, and buzzblobs. The enemy is in its own little world and has little or no reaction to what Link is doing or where he is on the screen in relation to their position.
• Constantly alert enemies. These are enemies whose AI has them always aware of and attacking Link's position. This includes usain bolts, ball 'n chain knights, beetles, and mini-helmasaurs.
• Enemies who are in a stasis, and when they are activated, usually by proximity to Link, they attack him directly. Examples include eyegores and ravens/murderdactyls.
• Enemies who have a patrol behavior, where they're unaware of Link, and an aggro behavior, where they're aware of and actively attacking Link. The enemy can move between these two states. This is how most guard-type enemies in the game work.

This page is about the latter AI type. The enemy has some patrol AI pattern where they walk (frequently with random directions and timers) and look for Link. When they detect him, their AI changes, and they will charge at Link or shoot projectiles at him.

Search probes

Search probes (sometimes called search beams) are the mechanic by which these enemies simulate "seeing" Link. In the direction the enemy is facing, they'll shoot out invisible "probe" sprites in a sweeping pattern. If a probe contacts Link, the enemy will become alerted to Link's presence and switch into their aggro mode.

One important interaction that can be puzzling is that ancillae, which are the objects spawned by Link's items and actions, can contact search probes. So for example, if you throw the boomerang at one of these enemies, the boom may hit a probe and return to Link early. In normal gameplay, this will appear as though the boomerang just randomly returned to Link before hitting anything, but it's because the boomerang has hit one of these invisible probes. This is often called a shortboom, and it most commonly happens with the boomerang. But it can happen with other ancillae as well.

Search probes are also used by beamos for determining when to fire a laser.

Audio detection

These enemies also have a simulated form of hearing. When certain actions occur, all currently loaded aggro-AI enemies will be alerted.

The actions that can trigger this:

• Bonking
• Tinking sword or hammer against a wall or an enemy's weapon
• Ancillae solid tile collisions (i.e. a projectile hitting a wall) for the following ancillae:
  • Boomerang
  • Bow
  • Fire rod
  • Ice rod
  • Lamp
  • Magic powder
  • Somaria beams (not blocks)
  • Sword beams
• Ancillae sprite collisions (i.e. a projectile hitting an enemy) for the following ancillae:
  • Boomerang
  • Bow
  • Cane of byrna
  • Fire rod
  • Hookshot
  • Ice rod
  • Somaria beams (not blocks)
  • Sword beams

Notably, the following things don't alert these enemies:

• Bombs and bomb explosions
• Slashes, dashes, pokes, or spin attacks (assuming there's no tinking)
• Using the flute
• Using the hookshot against solid tiles, whether the hook latches and pulls Link to the tile or the hookshot just tinks off of it
• Using the hammer without tinking
• Powdering an enemy