Prismatis or the Prismatic Shield Charm is another shield charm used in the First Year Army Battles, along with other students such as Nymphadora Tonks. It is first seen used by Draco in the Battle of Hogwarts Lake: "'Prismatis!' shouted Draco, raising his wand, and that shield you could see even through the water, a sparkling multicolored flat wall wide enough to shield Draco and the five other Dragons with him." (Ch. 33) As described, it glows a vibrant multi-colored hue, and can evidently be shaped many ways, as later in the same battle Harry is seen maintaining a "Prismatic Sphere". Prismatic shields cannot move with the cast as Contego can. "They couldn't use the Prismatic Shield while they were maneuvering, but Parvati Patil and Jenny Rustad were currently maintaining Contegos around the officer group..." (Ch. 67)
It can be condensed to become more durable, as seen when Tonks uses it to block a spell that would otherwise have smashed through a regular-sized shield. "...a small rainbow sphere formed in midair almost instantly, the miniature barrier so condensed and bright that it stayed intact even as Jugson's hex hit it and bounced off toward Belka, whose wand flashed to swat away the dark bolt; and then a moment later the many-colored blaze was gone." (Ch. 73) Prismatis seems to take much more magic to maintain than a Contego, as seen when Draco intended to wait until Harry tired enough to drop his shield in the Battle of Hogwarts Lake, whereas a Contego takes very little magic to maintain. It seems that stronger spells such as Elmekia will pass right through the barrier without destroying it, or perhaps this is actually the function of Elmekia itself. "'Elmekia!' shouted Lee and Parvati shouted 'Prismatis! ' and the rainbow wall formed but the fiery blue blast passed right through it like it wasn't even there."