Apart from the Ender Dragon which drops the most experience points, count on these hostile mobs for XP whenever you encounter them.
- Drowned
- Ravager
- Elder Guardian
- Guardian
- Evoker
- Witch
You always have a better chance of gaming more XP points after killing hostile mobs than killing tamed mobs. Although rare hostile mobs like Elder Guardian and Evoker tend to drop double XP points than mobs like Creepers and Zombies, which are more common during nightime.
Sometimes I often try to get out at night to explore new biomes or finds proper lands for new projects, so that I inevitably run into hostile mobs giving me good XP points.
Drowned
They are common underwater hostile mobs that drop 5 XP after they die. They swim pretty fast and can survive on land during night time and can be found near all water bodies. Drowned should be delt carefully if they have tridents. So be sure to keep a bow and arrow or a shield near you if you encounter one.
Ravagers
That beast of a mob can give you 20 XP points and a saddle upon death. Even if they are hard to kill and can take out 3.5 hearts out of your health bar, they swim pretty slowly. This can be used to your advantage by getting you some shots of arrow as it slowly swims towards you.
Elder Guardians and Guardians
Its the biggest underwater hostile mob that spawns inside ocean monuments only. You can try to pull out the Elder Guardian on land as it becomes much easier to kill it on the land. Either way its hard to fight and maintain your breath underwater.
If things went wrong and you do end up dying, and your respawn point is far far away, it might get hard to get back the things your items lost near the ocean monument.
Evokers
Evokers are hostile mobs that spawn on top floor of Woodland Mansions that are able to attack through blocks and can call the Jaws and Vexes for help. You get 10 XP , totem of undying and emerald after his death.
The Woodland Mansions are typically found near the Dark Forest Biomes.
Witch
Witches drop 5 XP along with glass bottles, Redstone etc after they die. They are less uncommon near Swamp Biomes and can be found near their swamp huts. They use ranged spells for attacking you. They are resistant to water and lava.
So if you have only set out for gathering experience points, try to go after much easier targets like creepers, zombies, skeletons etc instead of a witch that d
