Drag through neighbouring tiles (diagonals count). Open with an equal pair like 4,4, then each tile can be equal or double: 4,4,8,8,16.
Lift your finger and the chain merges into one tile at the end, worth the sum rounded up to the next power of 2. Drag back over a tile to undo steps.
Stages: the progress bar fills as you merge. At each stage the smallest number stops dropping and every one of it is cleared. A new, bigger number joins the drops.
Power-ups arrive at random each stage and keep until used, any time: Dynamite blasts a tile and its four neighbours, Wipe out removes every tile of one number, Random wipe zaps three random tiles at once, Show me the way lights up the longest chain on the board.
Mega blocks (gold ring) are huge. Bricks can't be used and only vanish when they reach the bottom. Frozen tiles stick in place and can't start a chain.
Chaos mode: new tiles are any number within 7 places of your highest tile, so the board is a free-for-all. Stages only hand out power-ups.
No equal neighbours left and no power-ups? Game over.