Minecraft wiki entry for Superflat_survival, associated text: Killing the outpost captain causes the bad omen effect, which gets raised by the number of captains you kill. Pillager outposts usually spawn 1-3 pillager captains. During bad omen, if you enter a village, a raid occurs. A raid is an event where illagers come to a village to kill villagers and the player(s). So if you don't want a raid, you can drink milk to remove bad omen or stay outside the village for 100 minutes.