Janus Marius
Plo Koon Rulez!
Actually, Mace "completed" Juyo by adding his own flavor to it. In a sense, he created a new form because of a new outlook and philosophy to it. The original form "Juyo" is a blend of the other five forms (Niman doesn't count in this) and strives to be unpredictable and force aided. However, in adding the element of Vaapad, Mace Windu changed the form so that it emphasis playing touch and go with the darkside without being corrupted by it. This is a stark contrast to Maul, who embraced the darkside, or Kavar, who likely avoided using it. In doing this, Mace applies an equilibrium to the form that it didn't possess beforehand.
How does this effect Juyo? Well, in a sense it doesn't; Juyo still exists, and it is the foundation for Vaapad's moves. The major difference is in fighting philosophy. Where Juyo strives to be a Jack-of-all-trades and add some randomness to the mix, Vaapad is random because the inner persona is riding the darkside without succumbing to it. It's essentially Juyo with veiled passion, and the end result is Mace having a leg up on other practitioners of Juyo who lack said passion and drive.
For more information, read the novel Shatterpoint.