Difficulty: 4 - Applied-Intermediate Trick
Siteswap: (6,6)(2x,2x)
Prerequisite Skills: 3-Ball Shuffle Switch, 4-Ball Sync
Watch Video - WMV - 0.6 MB

I like to add the "shuffle switch" exchange (2x,2x) to a lot of my tricks, especially any columns or sync patterns. This one is just adding the (2x,2x) exchange under the basic synchronous 4-Ball pattern.
Instructions:

First, practice the shuffle switch with 3 balls.

While juggling the basic 4-Ball Sync pattern, just throw one set a little higher than normal. While those balls are in the air, quickly exchange the two balls in your hands.

You may need to practice the (2x,2x) exchange by throwing one ball over the other.
Put it all together and you get a fun pattern with potential for a ton of variations.
Variations:

(6,6)(2x,2x)(4,4) - You may find it easier to do the shuffle switch every third throw.