The "Second Sentinel" is a character in the video game Hollow Knight: Silksong. It is a cogwork knight and automaton built by the Architects to protect the Citadel and its pilgrims. The Second Sentinel is found initially dormant behind a breakable wall in the west side of the Cogwork Core area in the Great Citadel. To activate the Second Sentinel, the player must collect three Cogheart Pieces scattered across Pharloom and assemble them into a Mechanical Heart, which is then placed in the Sentinel's body. After activation, the Sentinel comes to life and can be found roaming the Citadel, occasionally fighting enemies. The player can eventually initiate a boss fight against the Second Sentinel by starting the "Final Audience" wish quest from a Wishwall in Songclave. The battle takes place in High Halls and requires observing and dodging its various scissor blade attacks, including lunging strikes, aerial moves, and energy bursts. Defeating the Second Sentinel rewards the player with the Reserve Bind (a bench heal) and the "Eternal Devotion" achievement. The character is notable for its intelligence and design, with multiple attack phases and moves such as Gilded Combo, Aerial Lunge, Power Blade, Scissor Strike, and defensive parries.