Double Up

Double Up is a sliding puzzle about growing animals. You push every tile across a small board, matching animals join into the next bigger one, and you try to build the biggest animal of all.

How to play

The board is a grid of squares with a few small animals on it. The smallest is a ladybug, and the chain grows through a bee, chick, mouse, frog, bunny, cat, puppy, piglet, panda and bear up to the whale.

• Sliding: swipe on a phone, or press an arrow key on a computer. The letters W, A, S and D work too. Every animal on the board slides as far as it can in that direction.
• Joining: when two animals of the same kind bump into each other, they merge into the next bigger animal. Each merge adds to your score.
• One join at a time: an animal made by a merge cannot merge again during the same slide.
• New animals: after every slide that moves something, one new small animal appears on an empty square. Most of the time it is a ladybug, and about one time in ten it is a bee.
• Winning: make the goal animal shown at the top of the page. A card tells you that you made it, and you may keep playing to push your score higher.
• Ending: the game is over when no slide can change the board.

A slide that would change nothing does not count, so a wrong swipe does no harm. Your best score is saved for each level.

The levels

The levels change the size of the board and the goal animal.

• Easy: a roomy 5 by 5 board. The goal is the bear.
• Medium: the classic 4 by 4 board, with the bear as the goal.
• Hard: a tiny 3 by 3 board. The goal is the puppy, which is lower down the chain.
• Expert: a 4 by 4 board, but the goal is the whale, one step beyond the bear.

The project tested the levels with a computer player that plans two moves ahead. It reached the goal in nearly every Easy game, about 55 in 100 Medium games, about 23 in 100 Hard games and about 8 in 100 Expert games.

Today's game

The daily game is played at Medium. Everyone who plays on the same calendar day gets the same sequence of new animals, so the game starts and grows the same way for every player.

Tips

1. Pick a corner for your biggest animal and keep it there. Slide toward that corner and its neighboring side far more often than the others.
2. Build a row along the edge. Keep the animals in that row in order from biggest to smallest so they can merge one after another.
3. Avoid sliding in the direction that pulls your big animal out of its corner. If you have to, do it only when it is safe.
4. Do not scatter the small animals. Join them early, because a board of many unmatched animals fills up quickly.
5. Before each slide, glance at which animals will meet. Plan so that a merge makes room for a second merge.
6. On the small Hard board, there is little room. Look two slides ahead each time.
7. Keep one safe direction in reserve. When your main moves are blocked, you want a slide that does not pull your big animal out of its corner.

A bit of history

Slide-and-merge puzzles became very popular on phones and the web, where a single swipe is all you need.

Questions

Why did nothing happen when I swiped? No animal could move in that direction. The game ignores a slide that changes nothing.

Can I undo a move? No. Plan each slide with care, as each one is final.

Do I have to stop when I reach the goal? No. A card says you made it, and then you can keep going for a higher score.

Is it all luck? No. New animals appear in random places, but your choices decide how well the board holds together.