Endermites are like silverfish, except purple. They are technically slightly smaller, but nobody counts that. Endermites and endermen tend to fight each other.
The ender dragon is technically the final boss of the game, but people always play til after fighting it. To beat the ender dragon what you should do is shoot the end crystals on top of the huge obsidian pillars with projectiles, and then shoot it with a bow. Once it is defeated it will drop tons of XP and also will fill the end portal on the end island with portal blocks, and spawn a ender dragon egg on top. To get the egg what you have to do is right click it to move it somewhere on the end island, then 2 blocks under it place a torch. Then break the block under the egg. The egg will fall on the torch, which will drop it!
Shulkers are very annoying. You can not damage them if they block themselves with their box, and they shoot auto aiming projectiles that levitate you for around 10 seconds, meaning you wont be able to hit them unless you use your bow. To kill them hit them when they are not covered by their box.