I would imagine a mod that could make you choose your "race"

Dwarfs: Can craft "Dwarfen ingots" to make armor and tools using the "Dwarfen Forge" which are 5 times stronger than diamond and only Dwarfs can use. Dwarfs are only 1 block high, takes 2 secs to climb up a block, cant jump and start the game in a deep cave with iron tools and torches. they also can see in the dark! Quest is to find a stronghold and find the "Hammer of Kerath"

Wood Elves: Can craft "Elven Bows" and get poisoned if they eat meat. Can climb trees without vines and are 1 and a half blocks high. They start the game in a jungle with Glowing plants, Seeds and bread they also cant take fall damage. Quest is to kill a Demon
My Ignore List
Goblins: Can craft "Goblin" armor and weapons which are worthless. They eat only meat and get poisoned if they eat bread, vegetables or fruit. Start the game in a swamp village. Quest is to kill a NPC.

Humans: Normal steve, jumps 1 block, 2 blocks high, normal crafting. Start the game in a NPC village 'skins will be Steve and Stacy skins' . Quest is to find one diamond.

Demons: Can camoflage as fire, makes tools out of "Nether Ingots" and blaze rods, twice as much health, hard to kill, can break blocks with hands in the nether but not in the over-world, lava and fireproof but cant make armor, worst enemy of the wood elves. Their quest is to find a nether portal and kill at least one wood elf. Spawns in a nether stronghold.

Troll: The Ultimate Mob, 4 blocks high, spawns in mountains 4 times as much health, small hunger bar and has an area of effect attack when you click F. You can only use this mob when you have completed the 5 quests. No Quest

There is a quest tracker button next to the achivement button that tracks which quests you have completed.

The respective classes are the only ones that can craft their recipes; eg, A Human cant craft a Dwarven Forge.

Having different races creates diversity and a different playing experience every time. Playing as Steve all the time, and doing the same things gets boring after a while. Playing as a Dwarf then a Elf would make the player adapt to different situations.

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