Hi there, and thanks for checking out my game!
Concerning your question, the Blob movement is a "stacking" mode. Hitting the number keys changes the number of Blobs that form the stack, which can then be used to climb up or down. You can even quickly tap the number keys several times to add to the current number so that you don't have to reach for bigger numbers for bigger stacks. The main intention of this is to attack enemies that are out of reach: if you survive long enough, flying enemies appear and fire from above, which can make the grounded enemies more difficult to deal with. As you noticed, the drawback to this is that the Blobs you use in a stack aren't able to be used for attacking, so you can recall them with a right click.
Truthfully, the stacking system would have benefitted from even a basic tutorial, and I did want to make one, but I was already running out of time to finish the core gameplay (also the reason no sound was present), so I had to leave the instructions in the included readme/on the game page.
Again, thank you so much for checking this out. Your feedback is a great help too, so thank you for that as well!