Surprise is when something significantly breaks our expectations, usually in a very sudden manner. It's very easy to implement surprise in games. As designers, we tell the player what to expect, and so it's quite simple to suddenly break those expectations. However, carefully balancing the use of surprise within a game requires some consideration.
In Braid, the player solves puzzles by distorting time in a variety of manners. The protagonist of the story, Tim, is constantly trying to reach the princess, but she is always stolen away at the last minute. The story builds up more and more throughout the game with this cycle of almost rescuing her but never quite making it. The ending of the game is an absolute shock to the player, as it uses the very mechanics they've been employing the entire game to turn the story on its head.
In Silent Hill 4: The Room the player starts in their apartment and returns there after every level. Each time, they walk down a hallway and pass by the windows that they are likely to at see directly, or at least peripherally. The windows display a dismal, rainy city if the player looks out through them. This remains the same for many times, until one time later in the game a decapitated head silently drops past the window. This is a shocking contrast to the normal scenario at this point, and leaves the player significantly surprised.
When considering how to add elements of surprise into your game, consider the player's state of mind, the purpose of the surprise, and pacing.
Player's State of Mind
Consider the events that happened in the game shortly prior to where you intend to include a surprise. For example, if the game's atmosphere up to the surprising moment built up a great deal of fear or tension, a surprise at that time will be extremely shocking. Surprise can be used during times of low excitement to great effect because that is generally when the player lets their guard down.
Purpose of Surprise
What is the reason for surprising the player? It's important to consider this when adding surprise because meaningless surprises can actually disrupt the overall experience. The meaning doesn't have to relate to the narrative, but it should relate to the experience that the game is trying to convey. For example, in Silent Hill 4, the player can look out through the peephole of their apartment door. Almost every time there is nothing but an empty hallway, except one time when Walter, the main antagonist, is standing immediately in front of the door staring back at the player. The designers could have put any enemy in the game there for a surprising effect, but specifically placing Walter there had much more meaning within the game.
Players are extremely skilled at detecting patterns. It's what games teach us to do. If the player believes they can detect a pattern to the surprises in the game, they will then attempt to predict when the next surprise is going to happen. If they are correct, the event is no longer surprising. When implementing surprise into your game, think about when the most recent surprising event occurred or when it most likely occurred if it is random. Also consider the way that surprise was presented. As many properties of the surprise that can be changed should be considered for change, of course still keeping within the style of the game. It can also be useful to review pacing a final time after all surprises have been put in place.
Currently, no relevant metrics for measuring curiosity in games exist as of yet.
The lens is industry standard and empirically validated.
Components: The Player