Contrary to its name, the End island is not the most engame island in the game.
Players can kill enderman on 3 tiers, each tier having more health than the next, slowly going downward to the Nest.
Right before the Nest is the Void Sepulture, where players can kill very high level Voidling Fanatics. It is a very endgame section of Skyblock.
If players are not ready to enter the Void Sepulture, they can enter the Dragon's Nest.
The Dragon's nest is a mid to endgame section of the End island for players to kill Zealots, which drop Summoning Eyes. Similar to Arachne, you can place 8 of these eyes at the center of the Nest to spawn a Dragon. There are 8 types of Dragons:
Dragons may drop items ranging from Fragments(Certain amounts make the player eligible to craft a piece of armor), Armor Pieces, Scrolls(Unstable only), Dragon Claws (Used for upgrading items), Horns(Used for upgrading items, Superior only), and very rarely, the Ender Dragon Pet.
Another boss in the end is the Endstone Protector, spawned after the entire server has killed a certain amount of Zealots. It drops pet items and pets occasionally.
Image taken by me, created by the Hypixel Team