Tumblestone

The easier of the two nightmare bots achievements. The other one currently being impossible to the human soul.

To set it up, go into Multiplayer -> Private Match. Use up on the right thumbstick to put in Nightmare bots on each slot. Then press start (or select?) and switch the game mode to Tug of War. To make it easier, make sure that it is set to 3 rounds (the minimum).

The way the mode works is that everyone is given two puzzles to solve, if you solve the two of those before anyone else can, you win. If someone else solves one then another puzzle gets added to everyone's boards.

Since the puzzle is randomly generated, the first focus is seeing if there is any color that only has three pieces and sticks out right from the get go. Its a pretty easy decision to make, but it gets rid of pieces on the board and makes it less confusing. The same idea applies if there are six pieces of one color that you can get immediately. This should only take a second of thought. After that...

My method is simple, 80% of the time the mini-puzzle is set up in such a way where one of the colors (a group of 3) is blocked by solely another color (usually the color with the most pieces). You want to make an effort toward clearing your way to that one color first, and when you take care of it the rest of the board is simple. So focus solely on liberating one of the colors!

The problem comes the other 20% of the time, when that isn't the case. That is, two different colors are blocking that single color of three. The way I would look at it is in reverse, see how you can clear the blocks in the middle that block that single color and then how can you get to those middle blocks.

Hopefully that helps!

If not, here is a video of me beating the bots. If you want to study my gameplay further. The ones I breeze through are 80% of the time, the ones I get stuck on are 20% of the time.