When he casts spells or shapeshifts, he expends magic energy—this recovers in time, and can be replenished by drinking the blue blood of ghostly enemies. Conversely, undead opponents relinquish harmful black blood, and demons and mutants yield green blood which poisons Kain, causing his health to deplete at a swifter rate. Over the course of the main quest, Kain acquires many items and abilities, which facilitate increasingly nonlinear exploration. As he collects blood vials and rune pyramids, Kain's maximum blood and energy capacity rises. By drinking from blood fountains, he receives strength upgrades, faster magic regeneration, and immunity to weather effects. Weapons include iron and fire-elemental swords, a spiked mace, twin axes, and the Soul Reaver, a two-handed flamberge. Suits of iron, bone, chaos, flesh, and wraith armor feature, and each combination of equipment has advantages and drawbacks. Spells, in the form of magical tarot cards, are used in both strategic and practical contexts, their functions ranging from summoning artificial light to mind control and the evocation of lightning storms. Shapeshifting enables Kain to assume the forms of a bat, allowing for immediate travel to checkpoints; a wolf, with enhanced speed and the capacity to jump; a cloud of mist, which enables him to pass through gates and cross water; or a human, with which he can covertly interact with, or bypass, certain non-player characters. There are 100 secrets present in the game, logged if the player uncovers hidden areas, switches, and dungeons; these encompass spirit forges, at which Kain may donate a significant portion of his blood in exchange for powerful battle artifacts. A day and night cycle passes progressively—at night, Kain's attacks become more potent, and during full moon phases, some sealed doors become accessible. "Blood Omen" introduces the land of Nosgoth, a fantasy setting dominated by humans and vampires. The health of the world is inextricably connected to the Pillars of Nosgoth—nine supernatural edifices, each one protected and represented by a human guardian. These sorcerers collectively comprise the Circle of Nine, and if a member dies, a new guardian is called to take their place by the Pillars. Hundreds of years prior to the events of the story, the Circle formed and sponsored the Sarafan, an order of monastic warriors devoted to eradicating the vampire race, and in the game's prologue, the vampire Vorador reacts vengefully by killing six of the guardians and defeating Malek, the Sarafan leader.