Patrol

Patrols, known as pillager patrols $$, are common naturally spawning groups of pillagers

Spawning
Patrols spawn as a group of 5 pillagers $$ or 2–5 illagers $$ (all pillagers except in hard difficulty, which has a 20% chance for any pillager to spawn as a vindicator instead), one of which is the raid captain. The raid captain wears an ominous banner on its head. The other illagers follow the leader.

Java Edition
Patrols spawn in any biome (except mushroom fields and its variants) at light level 8 or lower, only at night, like monsters.

Patrols spawn naturally after the world age reaches 100 minutes (5 in-game days), then after a delay between 10–11 minutes an attempt is made to spawn a patrol with 20% chance of success; after an attempt is made the delay is reset.

Bedrock Edition
Patrols spawn around 24–48 blocks away from the player (or more than 48 blocks away from the player if they are in a village) in, ,, , , and biomes, as well as their variants on sand, grass block, podzol, coarse dirt or on snow. Although villages can generate in snowy tundra, patrols cannot spawn there. They can also spawn in giant tree taiga biomes, although villages cannot generate there. On Easy difficulty, patrols can only spawn at light level 0–7 on the surface. On normal and hard difficulty, patrols can spawn in any light level.

Patrols spawn naturally after the world age reaches 100 minutes (five in-game days), then after a delay between 5–6 minutes an attempt is made to spawn a patrol (20% chance of success), repeating the delay and spawn attempts.

In Bedrock Edition 1.13.0 Patrols spawn around 24–48 blocks away from the player (or more than 48 blocks away from the player if they are in a village) in any biomes except in, , and biomes. Additionally patrol can spawn in biomes where common monster cannot spawn such as in:

Patrol spawn on solid block at surface, like monsters. On Easy difficulty, patrols can only spawn at light level 0–7. On normal and hard difficulty, patrols can spawn in any light level.

Patrols spawn naturally after the world age reaches 100 minutes (five in-game days), then after a delay between 10–11 minutes an attempt is made to spawn a patrol (20% chance of success), repeating the delay and spawn attempts.

Behavior
Patrols seek villages, wander around, and attack nearby players, villagers (adult villagers only $$), iron golems, and wandering traders. The patrol members' heads turn to follow a player who looks at them or attracts their attention. A player who approaches within 10 blocks of the patrol provokes them into loading their crossbows and attacking, and pursuing if the player flees. The pursuit lasts until the player dies or gets far enough away.

$$ when one of illagers are attacked, than they will alert nearby illager within 10 block to attack same target in swarm, the attacker doesn't need to be player(can be any mobs) and the distance between attacker and patrol can up to 64 block away from alerted illagers.

The patrol captain always drops an ominous banner upon death.

Bad Omen
Upon killing a patrol captain, the player receives the effect for 100 minutes (displayed as infinite on Java Edition), which has no consequences unless the player enters a village. Upon entering a village, the effect is removed from the player and a raid spawns nearby after about five seconds. In Java Edition, the level of the Bad Omen determines the chance of enchantment on raid member's weapons, and additional waves. The number of waves depends on the difficulty.