How to breed predator-prey hybrids
First set up your yukkurarium in such a way that you have at least 3 compartments. The compartment between predator and prey should have a small compartment to serve as a gap to prevent baby predators from falling off the other side of the wall to the prey's territory and vice versa. While this is not really that important it can save you time if your hybrid is considered a prey species so you would want your initial hybrid to not get eaten right away.
Once you have a nice set up. Get orange, age acceleration and anti-mold diffusers. They are not necessary but the orange diffuser ensures your yus wont die of starvation if you are lazy giving them food because you are too busy breeding predators with prey species in a separate compartment.
Basically to ensure the prey yu does not get eaten, it is a good idea to manually cause the predator and prey to want to refresh with each other by placing them in a separate compartment and shaking them both so that they refresh. For maximum number of kos, you can repeat the process even if one of the two is pregnant for as many times as they dont explode.
Once they have bred return the predator yu in the predator compartment and the prey yu in the prey compartment. If you have two additional separate compartments you can leave pregnant predators in the predator maternity ward and the pregnant prey in the prey maternity ward.
With some luck you can get a predator-prey hybrid within a few minutes if you play at max speed. If you have bad luck it may take an hour (but that is rare).
Get a remilia or flan and a prey yu that you'll be mixing paste with.