Old Challenges:
1) Build a Cobble Stone generator.
2) Build a house.
3) Expand the island.
4) Make a melon farm.
5) Make a pumpkin farm.
6) Make a reed/sugarcane farm.
7) Make a wheat farm.
8) Make a giant red mushroom.
9) Craft a bed.
10) Make 64 stone brick's.
11) Make 20 torches.
12) Make an infinite water source.
13) Craft a furnace.
14) Make a small lake.
15) Build a platform 24 blocks away from the island, for mobs to spawn.
16) Make 10 cactus green dye.
17) Make 10 mushroom stew.
18) Craft 10 Jack 'o' lanterns.
19) Craft 10 bookcases.
20) Make 10 bread.
21) Collect 10 Ender-pearls.
22) Cook 10 fish.
23) Craft 10 Black Wool.
24) Craft 10 Gray Wool.
25) Craft 10 Light Gray Wool.
26) Craft 10 Lime Green Wool.
27) Craft 10 Red Wool.
28) Craft 10 Yellow Wool.
29) Craft 10 Pink Wool.
30) Craft 10 Green Wool.
31) Craft 10 Orange Wool.
32) Craft 10 Snow Golems.
33) Craft 20 Paintings.
34) Build and light a nether portal.
35) Craft 5 Gold Ingots.
36) Craft 16 Glass Panes.
37) Collect 50 birch logs.
38) Collect 64 arrows and craft a bow.
39) Craft 10 stone buttons.
40) Craft 30 stone slabs.
41) Craft 10 signs.
42) Craft 20 ladders.
43) Craft 20 fences.
44) Craft 20 fence gates.
45) Craft 10 levers.
46) Craft 10 trapdoors.
47) Craft 10 stone pressure plates.
48) Craft 10 wooden pressure plates.
49) Collect 64 bonemeal.
50) Craft 20 cobblestone stairs.

New Challenges:
51) Collect 64 iron.
52) Make a gold farm in the nether.
53) Cure a zombie villager.
54) Spawn an iron golem.
55) Use redstone in three contraptions.
56) Find a slime chunk and create a slime farm.
57) Make a lava aquaduct system.
58) Go to the end and defeat the enderdragon.
59) Find an elytra.
60) Spawn and defeat the wither.

WarrioCrisps' Challenges:
61) Create a four stage beacon
62) collect 64 purple glass
63) Build a villager breeding system
64) collect full diamond armour
65) Create a cow farm
66) create 10 sticky pistons
67) respawn and kill the enderdragon
68) Build a platform from the main end island to an end island far away
69) collect a stack of Emeralds
70) Collect 10 enderdragon heads
71) craft 1 tnt
72) Collect 6 different music discs
73) Get the mending enchantment
74) fish 64 Cod
75) Create 64 Slime blocks
76) dye a full set of leather armour
77) Collect 64 Chorus Flowers
78) build a platform at the top of the world
79) make a hopper
80) make 64 dispencers
81) create a pixel art of your minecraft skin
82) name something Dinnerbone
83) Get an emerald from a Librarian Villager
84) Build a platform 1000 blocks away from spawn
85) Build a 1x1 wide platform around the nether's borderwall
86) kill a total of 1000 zombies
87) kill a total of 10 witches
88) walk a total 200 Kilometres (124.27 miles)
89) collect 256 obsidian
90) Create a banner flag
91) Collect 64 Beetroot
92) collect 64 vines
93) Make 10 clocks and hang them on walls
94) Escape the nether border (Note: may be impossible)
95) Killed 100 shulkers
96) Get a sword with sharpness 5, Looting 3, Unbreaking 3, Fire aspect 2, knockback 2, mending
97) make 9 more buckets
98) Make a creeper your pet
99) Spawn and defeat 2 withers at the same time