A flip fluid simulation created in Houdini, rendered with Mantra.
I wasted so many hours trying to get the diffusion to work at the speed that I wanted, just to realize that I had a typo somewhere, and then after trying to tweak for hours found that the resolution of the diffusion field was way to rough. Happy that I got to learn more about fluid/smoke simulations though.
sim time: 2-3 hours
render time: 38 hours (this was because of the whitewater shader that renders volumes with a reflection lobe, not worth it for this)