Fortstopher IV lurks in the depths of the world born from Cal’s heart, embodying his warped emotions. This Negati is made from two parts that make up the whole, and he attacks by shooting chess pieces and missiles.
He opens up with launching his fists out at the player, which is followed up by him slamming the arena, launching the player up high and raising some tiles, and immediately firing 4 missiles at the player from 4 cannons just away from the arena. When he is enraged, he will summon copious amounts of chess pieces to constrict the player's movement for the next attack.
While his true form looks like chess pawn's head walking on two legs. The vessel takes on hybrid approach as the top half resembles a king and the bottom half resembles a castle decked out with a bunch of cannons.
- Method 1: When and if you are launched in the air from the ground slam with Floaty Flower active, fly into the diminutive entity.
- Method 2: If you were unable to do the above method in time [or have already performed it], use Paladin Puncher to knock one of the missiles into the castle and then attack the running king.
- Method 3: Attack a queen piece with Tackling Bull or Paladin Puncher from his rage attack and then chase down and attack the king.
- Quad Cannon: The vessel's facial appearance and crown resembles Quad Cannon.
- Paladin Puncher: Its disembodied arms belonged to Paladin Puncher.
- His appearance represents Cal Suresh's expert at chess before his first defeat because of how he is a chess piece of a king.
- His true form being tiny and cowardly may be a reference to chess, where the King is a piece with limited and slow movement since it only can move one pair turn, along with the fact that keeping the king safe and away from the opponent's pieces is an important strategy in chess.
- Fortstopher IV as a whole is a representation of both Cal Suresh's past glory and current state as a former chess world champion. The vessel is a representation of Cal's former undefeated winning streak and how his many defeated opponents feared him, as well as the ego he developed during this time. However, Fortstopher's true form is a representation of Cal's "true self", showcasing his vulnerability and the self-pity that he felt during his losing streak and ultimately the passing of his wife.
- He is the only boss consists of a duo (since both the true form and the vessel can move on their own).
- This is somewhat referential to castling, a move in chess where the king can move to a corner on their player's side of the board with assistance from a rook on both pieces first moves.
- Fortstopher's true form is the smallest Nega Boss of the entire game.