Knights in the Nightmare is a strategic shooter game that is heavily influenced by the RPG genre; the game follows both present and past events as the game reveals what happened at castle Aventhium to explain the current events. The plot of the game follows the player's Wisp and a Valkyrie who recruits fallen knights to battle against the oncoming tide of monsters.
It is the fourth game in the Dept. Heaven series and was developed by Sting Entertainment for the Nintendo DS and the PlayStation Portable (PSP).
Battles in this game must first be set up in two different selection screens before they can take place; the first screen is the Setup where the player can prepare for the upcoming battle. At this time the player can look at the stats and information of their available troops, equipment and special items which can be used. This is also the only screen where the player can level up their troops by distributing experience points to each unit; there is also an option to transfer the soul of one Knight to another Knight which may produce a stronger unit however there are many potential conditions in the game which influence the success of this.
Following this, the Tactics Screen is the final preparation screen where the player can select which units and items to use in this battle; the player is also able to view what enemies they will be facing during the battle.
The actual battle itself takes place in real time and on a grid; battles have some turn-based elements where they use a timer where time is deducted for charging attacks and for when the player's Wisp takes damage on screen. The Wisp is used in battle to give out orders to the Knights however it is also under attack by the enemy and the player must dodge all of their attacks. During combat there are two main methods of attack; normal attacks and equipment attacks. A normal attack will recharge the Magic Point meter which is used unleash special attacks and Equipment attacks will charge the Skill Attacks that can devastate opponents.
The Rush Count system has a variety of conditions which are activated once the hit counter has reached a specific number; this system can give positive and negative effects to the player such as regenerating the health of a friendly Knight or regenerating the health of an enemy.
Killing enemies in battle is important but the aim is to order their deaths across the Enemy Matrix so that they line up horizontally, vertically or diagonally on the Kill Markers. This system is not used in Boss Battles where the player is faced with a single enemy to kill.
Death in the game is permanent for Knights, it can come in two ways; by falling in battle or by running out of Vitality. Vitality is decreased when the Knight uses a skill and can only be regenerated by levelling that character up, by transferring their soul or through the Rush Count system.
Setup the battle – Strategically select Knights based on their skills and decide which equipment to bring to the fight
View the enemy – Look at the stats of the enemy army before the battle and adjust the Knights to better counter the enemy
Manage the battle – Stay in the middle of the fight and issue orders to Knights while dodging the enemy
Rush Count System – Take advantage of the conditions and defend against the enemy supporting conditions
Perma-death – Knights permanently die and there are limited ways to keep them alive
 Players liked:
- Great story
- Beautiful graphics
- The battles
 Players didn't like:
- Large learning curve
- Repetitive at times
- Tutorials not detailed enough