Cycle fly is the most predictable and basic fly enemy in the game, and its name reflects its easy-going cyclic nature.
Location and Behavior
Cycle flies are found only in the Forest level. They fly around at a slow pace in a constant circle. If one hits a wall, it reverses direction but stays in the same arc pattern.
Pay attention to it's speed and consistent nature. It should be easy to avoid when this pattern is mastered. However, if you do happen to accidentally hit one, it takes one damage as well and drops 1-2 crystals.