Hyrule Compendium Entry
Decayed Guardians are decayed variations of the Guardian Stalkers that have long lost their mobility. They are found buried in the ground, unable to move due to having no legs. Decayed Guardians appear inactive until Link approaches it, when they light up and aim their laser sights at Link in preparation to fire. They and are prone to malfunctioning after being attacked, firing off several lasers in rapid succession. If Link performs a Perfect Guard with any Shield on its laser, it is instantly defeated. If Link hits a Decayed Guardian in it's eye using a bow, it will temporarily stun it. Using Stasis + on a charging up Decayed Guardian will stun them afterwards, even if not hit during stasis. In Master Mode, Decayed Guardians will sometimes take slightly longer in their charge up phase before firing their laser to throw off link's timing.
A massive amount of Decayed Guardians can be found in the Forgotten Temple and will simultaneously take aim at Link the moment he enters the temple.
A Decayed Guardian drops between 4 and 6 of: