Patrol

Illager patrols (Java Edition) or pillager patrols (Bedrock Edition) are common naturally spawning groups of pillagers and vindicators that attack villages.

Java Edition
Illager patrols spawn as a group of pillagers and vindicators, totaling five all together. One of the pillagers or vindicators will be the raid captain. The raid captain wears an ominous banner on its head. The other pillagers or vindicators will follow the leader and then target the village.

Bedrock Edition
Illager patrol spawn as group of 2–5 illagers. On Easy and Normal difficulties, only pillagers will spawn, with one of the pillagers being the raid captain. On Hard difficulty, 80% of the illagers will be pillagers, while 20% of them will be vindicators. One of the vindicators or pillagers will be the raid's captain.

Java Edition
Illager patrols spawn around 200 blocks away from villages in, ,, and  biomes, as well as their variants on sand and grass block, or in snow with a block light level of 0–8 and a sky light level of 10–15. Illager patrols spawn naturally throughout the day or night after 5 in-game days. The illager patrols need to spawn in the right biome near a village, regardless if the village is mostly generated in an unusual place. (For example, if a village generates mostly in a dark forest but a portion is still in the plains biome, then the patrol will spawn in the plains area near the village.) A patrol will spawn near the village only if it has beds in place and at least one villager.

Bedrock Edition
Illager patrols spawn around 24–48 blocks away from player (or more than 48 block away from player if in 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, illager patrols cannot spawn there. They can also spawn in giant tree taiga biomes, although villages cannot generate there.

On Easy difficulty, illager patrols can only spawn at light level 0–7 on the surface. On normal and hard difficulty, illager patrol can spawn in any light level. Illager patrols spawn naturally after the world age reaches 100 minutes (five in-game days), then after a delay between 5–6 minutes an attempt will be made to spawn an illager patrol (20% chance of success), repeating the delay and spawn attempts.

Behavior
Illager patrols will circle inwards toward villages and then proceed to attack the village and try to kill villagers and iron golems.

The patrol captain always drops an ominous banner upon death.

Illager patrols will sometimes walk into a village the player is in and try to do a mini raid on it.

Bad Omen
Upon killing a patrol captain, the player receives the effect, 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.