A world that grows its own mod: wake the Morphic Heart, feed it, and it grows materials, machines, creatures, bosses, a guide and a goal that exist only in your world.
A new particle engine: smoke that billows and drifts, sparks that bounce, rain that splashes by surface, and embers that really light the blocks around them.
Fuse anything with anything: items, blocks, machines and creatures from vanilla and any mod become one new working thing with its own look, name and powers.
Storage you dig: pour a pond of brine, and every source block holds stacks of the items that fall in. Grow it, steep it, merge it and open it from anywhere.