Deep Blues consists of an entire chessboard of enemies. Defeat the King to win.
Pawn: Starts by moving down 2 tiles, then can move down 1 tile every 8 beats. Can attack diagonally downwards. When it reaches the bottom, it will be promoted to a Queen.
Bishop: Can move 1 tile diagonally every 4th beat.
Knight: Can move 2 tiles cardinally then 1 tile to the left or right (in an "L" shape) every 4th beat. Can jump over other pieces.
Rook: Can move 1 tile cardinally every 2nd beat. The left Rook castles with the King at its first opportunity.
Queen: Can move 1 tile cardinally or diagonally every beat. The red piece gets knocked back 1 tile when hit.
King: The King does not attack until all of the other pieces are killed, and will teleport away upon being hit prematurely (still taking damage). The King can move 1 tile cardinally or diagonally every beat. Gets knocked back 1 tile when hit.
In the Zone 1 variant, all pieces are blue, which have 1 heart of health. The King has 3 hearts of health.
In the Zone 2 variant, the Knights, Rooks, and Bishops can all be randomly replaced with red pieces. The Queen is always red, excluding promoted Pawns. These red pieces have 2 hearts of health.
In the Zone 3 variant, all of the Pawns and the King are colored red. The King has 5 hearts of health. Promoted Pawns become red Queens. These red pieces have 2 hearts of health.
In the Zone 4 variant, all of the Pawns, the King, and random Knights, Rooks, and Bishops are colored red. The King has 5 hearts of health. Promoted Pawns become red Queens. These red pieces have 2 hearts of health.
In the Zone 5 variant, all pieces are red. The King has 5 hearts of health. Promoted Pawns become red Queens. These red pieces have 2 hearts of health.
As with all bosses, Deep Blues is slightly randomized. On the beat the player enters the room, either a pawn moves (about 75% of the time) or one of the knights (about 25% of the time, and each is equally likely). If it was a knight, then the second beat is the first time that a pawn moves. After the first pawn has moved, on the next beat a second pawn moves on either its left or its right, then on subsequent beats the pawn moving is determined by continuing to cycle around the room either left or right, depending on the initial direction, and wrapping around the edge.
For example, if the b pawn moves first, then either the a pawn or c pawn will move next. If it's the a pawn that moves next, then the order of pawn movement will be b-a-h-g-f-e-d-c.
Throw one-shot kill
The king takes full damage even in his initial position (unlike Coral Riff). With enough damage, this allows a thrown weapon to kill the king before he castles on beat 8. For example, on Deep Blues 1 with a base dagger and a war drum, there is just enough time to beat the war drum 5 times for triple damage: 1 beat to step into the room, 1 beat to prepare the throw, 5 beats to hit the drum, and 1 beat to complete the throw, for 8 beats total. Throwing a bomb at him with the Grenade Charm will also one shot him in Deep Blues 1 and 2.
Rapier quick kill
With a rapier that does at least 3 damage lunges (for Deep Blues 1 and Deep Blues 2) or 5 damage lunges (for Deep Blues 3 and Deep Blues 4), it is sometimes possible to simply press up repeatedly until killing the king. Whether this works depends on the randomization described in the previous section.
Here is a partial table of which random layouts work with this strategy. The upper left corner indicates whether a pawn moved first or a knight, and which knight. The left side indicates which was the first pawn to move, and the top indicates whether the pawn movement is cycling to the left or to the right. A rule of thumb is to only attempt the rapier quick kill when a pawn moves first and it's either the d or h pawn or the pawn movement cycles towards the d pawn (instead of away from it).
The king and left rook both have a special first movement that is an exception to their usual movement rules, inspired by Chess's castling rule (specifically kingside castling). On the 8th beat, the first time either piece moves, the king jumps two squares left and the left rook jumps two squares right.
Unlike actual Chess, it's possible for one jump to resolve if the other is blocked, and each jump can complete even if there is a piece in between the start and end. These cases are rarely observed during normal play.
The movement priority for the pieces is, from highest to lowest:
- Original Queen
- Pawns & promoted Queens
Because promoted Queens keep the same movement priority that they had when they were pawns, when two adjacent pawns promote one after the other and the player is on the second row or above, the result can be two Queens stacked vertically, a dangerous formation.
If both bishops are adjacent to each other they move every two beats, instead of every four.