One block that needs nothing to be placed against: right-click into open air and it appears in front of you, so a walkway can be built out over nothing or down into water. It breaks in one hit and comes back to your hand rather than falling on the floor.
Generators, batteries, chargers and cables for Forge Energy. Nine generators that each run on something different, eight tiers, and an artificial sun that powers solar panels day and night.
Play under a name and skin of your choosing instead of your account's. Made for recording and streaming, so you do not need a second account to keep your own off the screen.
Carry a magnet, and dropped items and experience orbs within reach come to you instead of having to be walked over. It works from anywhere in the inventory or a Curios slot, and a right-click switches it off and on.
Light sources in all sixteen dye colours: lamps, slabs, panels, bulbs, fixtures, rods, a cased lamp, and a recessed spotlight with no thickness at all. Every frame follows its lamp's colour, or stays fixed black or white.
A world type that runs the Overworld from -2032 to 2031 and the Nether from -128 to 1023. Caves, ore and the Nether's roof follow the new bounds, and other mods' ores travel with them.
One tool where three would be: a paxel mines everything a pickaxe, an axe and a shovel each mine, and strips, scrapes, waxes off, tills and douses as they do. It is made from the three tools, so it lasts as long as all three.