Minecraft wiki entry for Advancement_guide, associated text: To weaken the skeleton and kill it in one hit with your projectile, you can hit it with another weapon for a certain number of times, until you can hit the skeleton with the projectile in one hit. You will get the advancement as long as when the skeleton is killed and it was hit by your arrow at last. If you have an iron sword, diamond sword, netherite sword, or any type of axe (except netherite), you can hit the skeleton twice with that weapon before shooting the skeleton with a fully charged arrow in one hit. If you have a wooden, stone, or gold sword, hit the skeleton three times with that weapon before shooting the skeleton. A bow enchanted with Power IV or V can kill a full health skeleton in one hit. Although arrows are the easiest to use, any projectile can be used for this advancement.