To add a ball (or anything that will merge), go to the "Merge" sprite and add or delete costumes, and the engine will take care of the rest. Please make sure that the costume name is the same as the costume number for all costumes (at least don't make the costume name a number that is not the costume number). It is recommended not to change the size of the ball as it is already the perfect size. To change the grid, go to the grid sprite and modify the tile. NEVER change the size of the tile. NEVER change the number of tiles or their position as this will completely wreck the engine.
This engine is going to be for the new version of Merge Ball. Overlap the balls to make balls with larger numbers. Let me know what you think of it in the comments. Feel free to use this engine for your game; no credit is required. All by me. :) Bug fix: If you move a ball, there is a 1 in 20 chance that a new ball will spawn on the ball you just moved. I fixed the spawning part of the engine, and it should be fixed. Let me know if the problem is still not resolved.