Bad Omen is a harmful (negative) status effect in Minecraft Java Edition 1.21.
minecraft:bad_omen
Give Bad Omen II for 60 seconds (Java Edition 1.13+; duration in seconds, then amplifier where 0 = level I):
Remove the effect from the nearest player:
Bad Omen marks you for revenge: walk into a village with it and a raid begins, while entering a trial chamber converts it into Trial Omen for harder vault runs.
Kill a raid captain, the banner-carrying pillager at outposts or in patrols, and Bad Omen applies for up to 100 minutes. Ominous bottles, dropped by captains and found in vaults, let you drink the effect on demand instead.
Drink milk before entering your trading hall if you carry Bad Omen, or the raid will trash your villagers. Deliberately triggering raids is the farming route to totems, emeralds, and saddles, so the effect is both hazard and resource.
The effect ID for Bad Omen is minecraft:bad_omen. Java Edition 1.13+ /effect commands use this namespaced form.
Run /effect give @p minecraft:bad_omen 60 1 to get Bad Omen II for 60 seconds. The first number is the duration in seconds; the second is the amplifier (0 = level I, 1 = level II). Remove it with /effect clear @p minecraft:bad_omen.
Bad Omen is a harmful (negative) status effect in Minecraft Java Edition, based on its registry category (harmful).
Kill an ominous-banner pillager captain at an outpost or in a patrol, or drink an ominous bottle. The effect lasts up to 100 minutes and triggers a raid when you enter a village.
Drink milk, which clears the effect and prevents the raid from starting. Without milk, the effect expires naturally after its duration or converts into a raid when you enter a village.