Chaser are movable spikes that attack Link in various Zelda games. Similar to Blade Traps, whenever Link steps in the direct pathway of the Chaser, it will start spinning towards him, usually moving in the same direction until it reaches a solid wall.
Oracle of Seasons
Oracle of Ages
The Minish Cap
In Four Swords, there are two kinds of Chasers: those that follow a straight path (and in this are very similar to Blade Traps) and those that chase Link. To escape a chasing Chaser, Link has to either hide behind something, e.g. a bush, or move out of their line of sight. They can be quite hard to avoid, since crossing its line of sight - which extends in four directions from the chaser to any obstacle - immediately triggers it, and avoiding a moving one is even harder, since it's line of sight is constantly moving (it can change direction anytime, not only after it has hit an obstacle). Both kinds retract their blades when in rest, making them appear as red balls/dots. They are mostly found in the Hero's Trial stage.