#threesstrategy

In the standard strategy that all of the Threesporn authors use, we fill the board starting with the upper left corner, with descending numbers along the first row. When we reach the end of that row, we sometimes have a choice: Put the next biggest number in the corner, or in the second row. More often than not, it's easiest to build up from the second row, like this:

You can see that this board is about to clear; after connecting the 12's, the chain reaction will continue all the way up to the 768's. In the process, the 24 in the top row will slide over next to the resulting 1536. Because of this behavior, we refer to this number in the upper right corner as the "chaser".

Generally, to the extent you can control it, you'll want the chaser to be a larger number than the rest of the numbers on the board at that point. Usually this means 24, 48 or 96 is suitable, but sometimes you are forced to keep a smaller number there. It's also best to keep the chaser larger than the number below it (if you're not building on that square), because this allows you to move material into those cells if needed. You can see that this is the case in the game above, since the 12 on the right is smaller than the 24 and is not involved in the building of the 192 to its left.

So the chaser functions primarily to solidify the board after a clear, and as a repository of spare material. That's great, but I've recently discovered a third important use for it: as a source of material in building other numbers. To use it in this fashion, you'll have to move it out of the corner, which I call "pulling the chaser."

Here's an example:

Notice that since the first three columns are locked, I can move the rightmost 96 down and guarantee that I will make a 384 in the second row to introduce into the top row. What you don't see in this example is that the previous three moves, I had filled in the bottom row with those 1's and 2's in order to make this possible. Fortunately, they'll still combine nicely, so I'm not messing up my board at all by doing so.

Here's another similar example:

Notice that it might be tempting to push left or right to combine those 1's and 2's. But either way would unlock the first column, which destroys this opportunity to bring the 96's together. In this way, playing to lock columns temporarily like this can be very non-intuitive: You don't want to allow numbers to combine like normal, at least in the vertical direction. But you do want them to combine horizontally, or your board will be just plain stuck.

In both of these examples, the chaser was used with numbers immediately near it, which might not be surprising: If you see two 96's, you might already instinctively pair them. But it can also be used any time it's the "missing part". For instance, in this GIF, it's used to build a 96 in the second row, pull up another 96 from the third row, and insert the resulting 192. Snazzy!

You can see that the 48 was exactly the material that was missing there, so it made sense to rope it in.

Sometimes you need to pull the chaser to build something in the third row. Take a look at this example:

Here, I needed to make another 24 on the left, and a 2x3 grid wasn't going to be enough space to guarantee I could do that. I couldn't immediately shift down because of the third column, but could lock it by shifting up first. Then by moving down, I could line up the 12 with the two 6's to make a 24 and clear the board, making a Whalend. It would have been nice here not to move the chaser, but if you have a guaranteed chance to clear the board like this, you usually want to just do it.

There's one final type of scenario where pulling the chaser is smart:

In this situation, I have a plus block incoming, which would probably make a better chaser than the 12 I currently have there. Moving right wouldn't have been a bad option, either, but I also liked how the 12 fit into the second row.

Finally, a bit of a warning. If you don't pull the chaser, you might find yourself moaning in agony at your lost opportunities like this: