A Fixed Encounter, also known as spiked tiles when referring to games comprised of sprites, refers to a method of entering a battle. Fixed encounters differ from the basic Random Encounters due to their fixed nature; a fixed encounter starts when a player steps on a certain tile or interacts with a certain object.
Fixed Encounters is the normal method for engaging in a boss fight, and will occasionally be accompanied by dialogue, scripted actions or, in later titles, cut-scenes.
There are two common uses for fixed encounters, the first being to enter a surprise battle against bosses or stronger enemies. The second use is to impede the player, or to protect an area such as a Treasure Chest. While fixed encounters are a more common feature in the earlier games, they still have appeared in later games in the series. Fixed encounters cannot be protected against with No Encounters abilities.