The silver basilisk, or regulus platinum, is a rare subspecies of basilisk that humans have hunted almost to extinction. Silver basilisks were once common in Toussaint, and in Blood and Wine Geralt can still encounter one of the last of their kind.
Combat strategy
Take Golden Oriole against its venom and use Draconid oil. Aard can knock it out of the air and Igni works well once it is grounded.