Unstable Caves
M BLOC

Some stones may cave in if punched, making underground expeditions more risky.

Tac Nayn
GreenXenith

Adds Nyan Cat's evil twin, Tac Nayn (and a gray-scale rainbow).

Purple ore
X-DE

Adds new purple ore to floating islands and caves from height 200 to 31000.

New Biomes
Arkatron

If you like underground biomes, this thing is for you.

Noriel Sylvire's Minerals Core Modpack
Noriel_Sylvire

An API for automatically registering recipes, nodes and ore generation.

Trucraft
mt-mods

An alternative crafting system done entirely in the world.

Sun Flowers
Hybrid Dog

This mod generates flowers which close their heads at night.

Archaeology
SkyBuilder1717

Adds an looting and API in archaeologing

treasures
ademant

Treasure nodes with useful items

Obdy
Sires

Adds some pretty OP tools :)

Easter Eggs / Ostereier
Ineva

Adds various coloured eggs for Easter!

golden lava
GigaByte

add golden lava

Dirt Tunneler
Neuromancer

Makes dirt deeper and you can tunnel through it just by walking through it. Press spacebar/shift to tunnel upward/downward with auto placed ladders.

Mud
Blocky Player

Adds stylish mud blocks and even blocks you can walk through. Setup traps, secret rooms and much more!

Silver
Jackknife

adds silver ore and tools

Too many ores
TeufloV

This adds 53 new ores. But most of them are useless.