(I know, technically, it should be "serp" and not "slerp" but "slerp" is more fun to say.) Anyway, after several hours of reading wikipedia and playing with graphing calculators, I'm admitting defeat and posing this problem to the community. I've drawn out a diagram to help visualize what I'm asking if you don't know what I mean by "standard easing curves". The top left graph, shows the lerp function we already have, and the other three show the curvy variations of the three most common easing curves found in many programs. slerp() is of course sine interpolation which is useful across the board, glerp() is "gradual" interpolation, which is really good for audio, and flerp() is "fast" interpolation which is situationally useful also... I was actually a little surprised to find that these functions were not already built in to GMS2 next to lerp() but I apparently don't remember enough math to figure these out myself, so: Designing a slerp() function that works exactly like the lerp() function but curved. How math?