Cero Doble , Cero Oscuras and Cero Sincretico

Cero Doble 

   Spanish for "Double Zero", Japanese for "Heavy Performance Hollow Flash") is a variation performed by Nelliel Tu Odelschwanck, by swallowing her opponent's Cero and returning it back to the user along with her own Cero, making it more powerful.

Nel Tu using Cero Doble

 Cero Sincrético

     Spanish for "Synchronized Zero", Japanese for "United Hollow Flash" is a variation performed by Dondochakka Birstanne and Pesche Guatiche. Pesche and Dondochakka charge their Cero simultaneously and combine them, forming a large, swirling sphere. They then fire the combined Cero, launching a multi-colored beam. However, it does seem to greatly drain Pesche and Dondochakka---both are panting and on the point of collapse after performing it.

Pesche and Dondochakka using their Cero Sincrético

 Cero Oscuras  

     Spanish for "Dark Zero," Japanese for "Black Hollow Flash" or more grammatically correct Cero Oscuro, is a black Cero used by Ulquiorra Cifer in his Resurrección form. He also compares it to Ichigo's black Getsuga Tenshō. It covers any exposed light into pitch darkness. Ulquiorra also referred to it as "our Cero." The Cero Oscuras' range is vast, and its attack power is massive. It is powerful enough to shatter Ichigo Kurosaki's entire Hollow mask and critically injure him in the process. It is strong enough to destroy half of the dome over Las Noches. The superior Cero Oscuras is far greater than an average Cero. 

Ulquiorra using his Cero Oscuras against Ichigo.