I have vector A and vector B.

I want to get a vector that is between those two vectors (for example -100 units from point B)

Any idea how I can accomplish this?

You just take the average of the two. Is that what you want? That will be exactly the point in the middle between A and B.

Or, if you want it to be on the line that goes through A and B, and be at a distance of 100 from B, then you’ll need to get the direction from B to A, normalize it, and multiply it by 100. The direction is given by A - B.

This is what I need, many thanks

Okay. Just to be clear: The resulting vector you get, you have to add to B