Minecraft wiki entry for Advancement_guide, associated text: To get this advancement, you will first need to kill a drowned holding a trident. Drowned can be found in ocean ruins or underwater in light level 7 or less in ocean biomes (except in warm ocean), and river biomes. Zombies can be converted to drowned, but they do not spawn with a trident. Tridents are a rare drop from drowned, so you may need to kill a few drowned to get the trident. 6.25% of drowned spawn with a trident, and there is a 8.5% chance for the drowned to drop the trident, with an 11.5% chance to drop with Looting III. A shield can be helpful fighting drowneds underwater, as their tridents deal massive damage.