Worlds in neighbouring slots of the same type boost each other by 40% each. Tap a slot, then tap Equip on a world.
Permanent upgrades bought with Dark Matter. A Big Crunch resets them. Hold any row to see what it does.
Three separate saves on this device, saved automatically. Keep one as a throwaway to test and reset. Export and Import use the slot you are playing.
Every achievement gives +1% to all stardust income, and new ones keep appearing as you grow.