Combat has the most Islands, as of v0.8, compared to the number of farming isalnds and mining island and foraging islands. There are 4 combat islands:Graveyard, Spider's Den, Nether Fortress and The End
In the Graveyard ther are only zombies, zombies and ZOMBIES. The normal zombies with no armor have more health but go way slower than the zombie villagers with leather armor, who have less health.
In the Spider's Den, there are spiders(DUH), skeletons and slimes. Unless you have a Spider Sword (Weaponsmith) or better, and some armor that gives at least 100 defense, don't go there.
Basically the Nether in Minecraft Vanilla.It has Blazes, Pigmen, Withers, Ghasts and Magma Cubes. To survive there, you should use Fire and Lava Talismans and/or Campfire Badge. You can mine Nether Bricks, Netherrack, Glowstone and Quartz there.
In Vanilla Minecraft, there is 1 type of Ender Dragon. In Hypixel Skyblock, there are exactly 7 dragons: Old, Protector, Young, Unstable, Wise, Strong, Superior. Each drop the corresponding dragon fragments, and it requires 240 of one type of fragment to craft Dragon Armor. The Dragons can be summoned at the Dragon Nest. The Aspect of the Dragons can be obtained from killing dragons as well. Holy Dragon Fragments can be bought from the Bazaar, which is an NPC you can use after unlocking:Combat 7,Foraging 7 and Mining 7.