Silverlight

Silverlight is a magical sword used in the Demon Slayer quest, which can be kept afterwards. The sword can only be obtained by talking to Sir Prysin in Varrock Castle at a certain point during the course of Demon Slayer. He will send the player on a quest to obtain the 3 Silverlight keys to the box that Silverlight is held in - once the player acquires these keys and brings them back to Sir Prysin, he will give the player the sword. It is described as "a very shiny sword". This weapon cannot be made by players using the Smithing skill. If Silverlight is lost during the quest, it can be regained from Sir Prysin for free. Afterwards, a player must pay him 500 coins to regain it. A player can use the Drop trick to get several Silverlights. It can be sold to the Wise Old Man for 80 coins.

Silverlight is dyed black during the course of the Shadow of the Storm quest and later becomes Darklight after killing the demon Agrith-Naar. Both Silverlight (not Black Silverlight) and Darklight can be mounted on the wall inside of a player's POH if he or she has a Quest Hall.

Silverlight is similar to the steel longsword in terms of statistics - with the exception of the +1 magic defence bonus and being -4 in strength bonus - when fighting non-demon monsters. However, while fighting Lesser, Greater, Black or Abyssal Demons, along with demonic creatures such as Nechryael and Bloodvelds and Pyrefiends and even unique, high-level demons such as Zakl'n Gritch, Othanian, Holthion, Tstanon Karlak, Balfrug Kreeyath and the Ice Demon, Silverlight increases damage to approximately the same level as a rune longsword. However, Silverlight fails to have its special powers effective against minor demons such as Imps or demon hybrids such as Hellhounds. For example, what would normally be 110 LP damage against non-demons becomes 170 LP damage against demons.

However, because of Silverlight's low accuracy it is recommended that you DO NOT fight demons with Silverlight, unless you either can't wield rune weapons or any weapon that has superior stats to Sliverlight. Silverlight is one of the strongest melee weapons available to a defence pure or any other player with only 1 attack.

History
A group of Zamorakian Dark Wizards seized control over the Stone Circle south of Varrock from the druids of Guthix in the Year 19 of the Fifth Age, when the incredibly powerful demon Agrith-Naar, having bypassed the Edicts of Guthix set against him after the God Wars, disguised himself as a human dark wizard. Agrith-Naar led a ritual that brought forth Delrith, a colossal demon of terrible power, from Zamorak's realm, seeking to destroy Varrock in Zamorak's name.

Fortunately, a man named Wally happened to be outside the gates at the time, arriving at the Circle just as Delrith was being summoned by the cult of chaos druids. The god of balance, Guthix, despite his millennia-long slumber, sensed the disruption of balance caused by Delrith's summoning, intervened and imbued the sword of a fallen knight with his power, causing Wally to find it. Wally, after wielding the blade, which he had discovered in the recently created Varrock Sewers, stabbed Delrith with Silverlight and, with the assistance of a magical spell that he had received in a mysterious series of letters, trapped him within the stone block at the centre of the Stone Circle. Despite this victory, the Circle has remained in the control of Zamorakian wizards ever since, despite druidic desires to reclaim the circle lasting to this day. Wally died some time after his renowned triumph, but, his greatness has never been forgotten, and is honoured as one of history's greatest heroes. Sir Prysin, his most recent descendant, inherited Silverlight and placed it in the Varrock Palace for protection.

After one hundred and fifty years, the ancient Guthixian Gypsy Aris of Varrock, after offering to read the fortunes of a random human adventurer, discovers that Delrith is being summoned once more by a dark sorcerer at the Stone Circle, and after telling the human of Delrith's first summoning and attempted assault upon Varrock, along with how Wally wielding Silverlight was able to banish him, informs the adventurer it is their destiny to use Silverlight and save the world from Delrith. Wally had passed it down from father to son, until the surprisingly renowned knight serving King Roald inherited it. However, Roald, knowing that the risk of Silverlight falling into the wrong hands was too great to leave it unguarded, had Prysin put it in a special box that requires three different keys to open. Sir Prysin then, on the orders of the king, despite his own reluctance, entrusted two of the keys to Captain Rovin of the Varrock Guard and Wizard Traiborn of the Wizards' Tower, respectively, while keeping the third, bearing it upon his very person to safeguard it, until he accidentally dropped it in the kitchen drain. The human adventurer, with great effort, succeeds in locating all three keys, retrieves Silverlight from Prysin, and confronts the Dark Wizards and Agrith-Naar at the Stone Circle, causing Agrith-Naar to flee at the very sight of the legendary weapon. Though Delrith is nonetheless successfully released in time, he is still weak from his movement between dimensions, and the adventurer, uttering the incantation Gypsy Aris had taught them, manages to slay Delrith for good, sparing the city from destruction a second time. The mighty hero of Varrock, slayer of Delrith, is honoured highly as the saviour of perhaps all Gielinor, and from his recounts of his battle against the demon, a replica of Silverlight is produced and kept within Varrock Museum, and a new legend is written in the history of RuneScape. However, the power of the ancient blade will be required again when a demon with power surpassing even that of Delrith's own might emerges as the next great threat against Gielinor...

Trivia
Silverlight Silverlight
 * Silverlight can be traded on RuneScape Classic.
 * It is possible to keep Silverlight after Shadow of the Storm; one way to achieve this is to have Silverlight in your bank while you use another to kill Agrith-Naar. Another (much easier) way is to obtain Silverlight normally from Sir Prysin with no membership, even after completing Shadow of the Storm. (As a member, you can ask Sir Prysin to sell you silverlight instead of Darklight, but he wont sell you a Silverlight unless your account has no member credit.) Also, if you have mounted your Silverlight in your POH before Shadow of the Storm, the monk at the start of the quest will exclaim and give you another one.
 * In RuneScape Classic, Silverlight was sold in the Legends' Guild. This was the only way to re-obtain it at that time, and due to complaints about this, Silverlight was removed from the Legend's Guild and it was obtained from Sir Prysin from then on.
 * Due to its broad blade, exaggerated bevels and long fuller, Silverlight would probably classify as an XIa on the Oakeshott Typology scale.
 * Silverlight is one of only 2 free-player weapons given an actual name, with the other one being Eek the Spider, and one of the few weapons in the entire RuneScape game to have been given one.
 * Oddly enough, the Varrock Museum display plaque calls Silverlight a sword made of steel. This cannot be simply because Silverlight may be used to slay Vampyres, which can only be hit with weapons made of silver. However, the reason Silverlight is able to harm vampyres despite being made of steel might be Guthix's power in enforcing balance, seen in the effect of Silverlight on Delrith and the effect of Guthix Balance potions on vampyres. It is also possible it is a silver/steel alloy, similar to silverthril.
 * In While Guthix Sleeps, it is revealed that Movario, greatly fearful of the unnaturally powerful 'tormented demons', intends to seek out Silverlight in the event the sinister Lucien sets them on him, for "normal weapons will be only marginally useful, as the creature seemed to possess some sort of magical defense."
 * In RuneScape Classic, Silverlight will weaken a demon if it is used on the first hit.
 * Silverlight was graphically updated on 15 December 2009. Black Silverlight and its upgraded counterpart Darklight was updated along with the release of the 2009 Christmas event.
 * The Silverlight copy in Varrock museum did not change in the graphic update, it still had the look of the old Silverlight. This has been fixed.
 * The RuneScape logo has a sword in the middle, it strongly resembles (and could be) Silverlight. This is further hinted by how Silverlight originally resembled the RuneScape icon prior to its graphical update, and after the graphical update of the sword, the RuneScape icon also changed to resemble the updated weapon.
 * There is a glitch after the quest is complete (and possibly during) if you you use Silverlight with Sir Prysin your character will say " I've got one of the keys!" and Sir Prysin will tell you to keep it until you have all three. However, the same happens for most items, this can happen even before the player starts the quest or even heard of it! This glitch has not yet been fixed.
 * Along with the graphic update, its case was also changed.
 * Despite its reputation being a magical blade that is used to slay demons easily, it is actually quite a weak weapon considering its bonus stats when used to fight other monsters.
 * Interestingly, Silverlight has a green gem and hilt similar to that of metallic two-handed swords.