Minecraft 1.21 update is set to bring several changes to existing features, one of them being village raids. Raids are events that occur inside a village when you enter the area with a bad omen status effect applied to you. You can either run away from a raid and leave the village to perish, or fight through hordes of villagers and protect them.
In the Minecraft 1.21 update, however, the method of starting a village raid has been drastically changed.
Steps to start a village raid in Minecraft 1.21 update
1) Obtain an ominous bottle
Previously, you could get the bad omen status effect just by killing a raid captain (Pillager with an ominous banner on its back). This mechanic will be completely changed in the Minecraft 1.21 update.
Mojang Studios introduced a new ominous bottle that will give the bad omen status effect for one hour and 40 minutes. This bottle can only be obtained from trial chamber vaults or by killing a raid captain.
You can find trial chambers by exploring the underground caves in the Overworld. Once found, you must fight several trial spawners that summon various hostile mobs. One of these spawners has a small chance of dropping a trial key, with which you can unlock vault blocks. These blocks have an 18% chance of dropping an ominous bottle.
On the other hand, raid captains usually spawn with a pillager patrolling group. These groups can spawn anywhere in the Overworld, except in mushroom fields, when a world is older than 100 minutes. Once a raid captain is killed, it will drop the ominous banner and new ominous bottle.
2) Drink the ominous bottle and enter a village
When you obtain the ominous bottle, you can drink it to get the new bad omen status effect in Minecraft 1.21 update. This effect can vary from level one to five, which determines the difficulty of the raid.
After drinking it, you can find a village and enter it to start another new status effect called Raid Omen. This effect is essentially a countdown to when the raid will begin. You will have 30 seconds to either prepare for the raid or flee the village to prevent it. Once the raid omen expires, the village raid will begin.
It is worth mentioning that all these status effects can be easily removed by drinking a bucket of milk.