Downhill bunker shots can be troublesome for lots of beginners and even intermediate players. The process though is still actually quite simple once firstly understanding how to safely exit the bunker in the first place. Just remember the basic fundamentals in the bunker which is to have the stance quite wide, aim your feet left with the clubface pointing around 45 degrees right of your target. The ball position should be just forward of middle.
The object then is to aim around an inch behind the ball with a reasonably long backswing and follow through. The more you open the face for a bunker shot or lob shot will require you to swing longer as the ball will go higher with shorter distance. When you add sand into the equation it will require you to add even more speed through the ball. You want also use the bounce of the club which is the middle section of the bottom of the club.
Now when you're on a downslope which is the same for any shot in golf, you will need to tilt your body at the same angle as the slope. In terms of the swing you want to feel like you're hitting down with the slope. The ball will tend to come out lower therefore try and get your most lofted club for this type of shot. Also it may be hard to get the ball close if the flag is just tucked over the lip so just settle with the fact that the ball will probably run out 15-20 feet.
Lastly hit the bunker shot like any other bunker shot in that you want to fold up your arms after impact so that you can you still use the bounce effectively. This will help you generate maximum spin with a shallower divot. If it's a plugged lie scenario then you would need to play it slightly back in your stance with a square clubface. This would mean that your ball would come out low with not much spin. Your ball would then most likely run out a lot more pass the hole depending on the hole position.
If you'd like any further help with your bunker shots just book in a golf lesson with myself. We would conduct the lessons at Emerald Lakes Coaching Centre.