The Crystal Viper is a late-game boss enemy encountered in the last two Acts of Vanquish, and one of the Order of the Russian Star's most advanced RIs. It resembles a muscular, bald, nude man only slightly taller than a Gorgie, marine, or Sam made entirely out of glass or a reflective metal.
According to intel provided in the game, the Crystal Viper is an assassination unit that utilizes a crystalline body designed both to make it invisible to the naked eye and reduce the effects of optical weaponry on it. It is armed with a sword similar to the Bogey and utilizes some kind of electric/electromagnetic discharge system with no visible weapon which can both be used for electrical damage and as a sort of telekinesis to grab Sam with. When damaged, even if both its arms are removed, it can use this same electric discharge to reassemble itself. However, it appears to be unable to self-repair, as it cannot regenerate health in the two encounters Sam has with these units.
There are only two Crystal Vipers encountered in Providence: the first is on the Grand Coulee Dam and the second is within the colony's center. Both are fought alone with only a few Gorgies for support.
At a distance, a Crystal Viper will charge Sam with its sword ready. This can be countered with a button prompt, damaging it and leaving it immobile and vulnerable for a period of time.
Optical Weapons are useless against the Crystal Viper because of its shield and also because of its ability to disappear from the naked eye. Using ARS mode, the ARS Suits EMP melees and then barraging it with fire are the only way of damaging and killing the Crystal Viper.
- Due to the Crystal Viper's appearance, many fans have dubbed it the Silver Surfer for its resemblance to the Marvel comic book superhero. Others compare it to Dr. Manhattan, a character in the DC graphic novel Watchmen who has a very similar appearance and abilities to the Crystal Viper, down to being a shade of blue, capable of conjuring objects out of thin air, and capable of manipulating energy as an attack form without any sort of weapon. It also bears similarity to Ultimate Electro from both Marvel comic's Ultimate Spiderman series and Spiderman: Shattered Dimensions.
- Sam derisively calls the first Crystal Viper a "chandelier" and in an act of lampshade-hanging, later quips that it appears to be something out of "a bad video game."
- Crystal Vipers appear to have an extremely high energy requirement to function, as the first Viper's death results in a massive explosion which greatly damages the Grand Coulee dam but does not seem to have ill effects in the center of Providence.