All of these suggestions you have a greatly vague, unorignal, redundant and OP. Every mob you listed is redundant and OP, from the Magic Wizard, to the Skeleton King, to even a Dog, something that's already related to an existing animal, the Wolf.
The items/blocks you listed are also redundant. The glowgem is basically like Glowstone, but "glows too much". I'd be interested in new blocks that light up, but this is basically so similar to Glowstone unless you elaborate. The Collar is also redundant, and isn't needed because it's already applied to Wolves once tamed and can be dyed already. The Zeus Sword is so ridiculously overpowered, easily killing a fully enchanted diamond armored opponent in just one or two swings. And the Diamond Apple is a just a silly upgrade of the Enchanted Golden Apple. You're basically taking away the one thing that makes gold actually useful and replacing it with this, way more overpowered item.
The Magma Sea doesn't sound that needed, and if it were to appear in the Overworld, then that's a really bad idea, because it would just be a giant pool of lava for no reason and can burn down forests and grass. It's better off in the Nether, which in fact, there is already a Lava ocean. The Dark biome doesn't seem to have anything interesting about itself, other than having atmospheric bat, which despawn overtime, in a biome where light never touches it. Another thing is, what you have made is known as a wishlist, which is against the rules.