I came up with this trick ages ago & at the time I thought it was very similar to Burke's Barrage. This variation sees a Slam added on the side. Thinking about it now it isn't really a variation of Burkes Barrage but of the Pass under shower.
In this pattern there are a lot of things happening all at the same time, which makes it very hard to explain. But once you know what goes where it is an easy pattern to learn.
Start with all three balls & juggle a cascade. Pick a ball & throw it straight up at the side of the pattern. With the opposite hand throw an Over the top throw then reach over & Claw the first throw at its peak. Carry this ball in an arc back over the pattern from inside to outside. At the same time make a vertical throw with the other hand under the carry on the opposite side of the body (this should feel a little like an Under the arm throw) before catching the second throw. When the under arm ball peaks you should finish the carry at a point directly above it. Then simultaneously do two things. One, slam the carried ball into the opposite hand & claw the under arm throw all in one movement. & Two, empty the other hand to catch the slam by throwing it over the top again. Settle back into a cascade.
Do the same again starting with the opposite hand to before. Practise on each side alternately until you are comfortable.
Then you can put the two halves together. Focus your attention entirely on the ball that you carry & slam into the other hand. When you catch the slammed throw, carry it in an arc over top the ball which was thrown to empty the hand ready to catch the slam. Make an under the arm throw & slam again. The rhythm you need to say to yourself is, "Slam, carry, slam, carry..."
& just keep going. When juggling the full pattern be careful not to knock the underarm throw with the elbow of your opposite arm as you make the carry.