Spawn the Wither.

Cure a zombie villager.

Create an Iron Golem.

Smelt wood trunks using charcoal to make more charcoal.

Swim in lava while having the Fire Resistance effect.

Craft and place a sign.

Acquire 30 Emeralds by trading with villagers or mining.

Breed two cows with wheat.

Build some bookshelves to improve your enchantment table.

Kill the Enderdragon.

Enter an End Portal.

Destroy a Ghast with a fireball.