Of all the Type Zeros encountered, there were only three recorded cases of SS-Class. Of the three, Cross Eye Alpha and Beta were especially terrifying in that they worked as a pair, bringing unprecedented offensive power to any battle they participated in. As a pair, they were also armed with Balisarda, only the second time a Beast was equipped with a Weapon of Massacre.
Their terrifying offensive power could cut down multiple frigates at the same time and bring down a Heavy Battleship in an instant. (ME0-Ch26, Ch27) Yet these two Beasts were not glass cannons, being able to project shields so strong that they could withstand Anti-Fortress Class firepower from three G-34 Satellite Cannons without any apparent harm.
As the AE was pushed to the breaking point, there was an all out assault to prevent E-99 and E-101 from taking any more planets. This was the decisive Battle of Velchees, where despite all odds that just a pair of Knights would last minutes, after various Master Knights and Order Chiefs had been killed, they were defeated by the Top Sword Pray and her student, Anne.
In the prologue of ME0, it was revealed that Cross-Eye Alpha is still alive and retreated to a remote planet in space. It's currently unknown why it was cloaking a 1500km satellite above this planet using Balisarda.