Hoppers are monsters found frequently in The Basement, less frequently in The Caves, and very rarely in The Depths. Generally, Hoppers aren't agressive and jump randomly around the room. They can notice the player only within their jump distance.
Hoppers are common enemies that deal normal damage on contact and have similar health to Gapers and move relatively quickly. If the player is within a Hopper's jump range, it will jump towards the players. Pairs of Hoppers will be spawned by Greed during its boss fight.
F. Hopper Edit
After touching a Fireplace, Hoppers will become F. Hoppers.
F. Hoppers behave similarly to normal Hoppers in that they will randomly hop around the room, following Isaac only when within a certain range. Unlike normal Hoppers, F. Hoppers will follow the player within a much larger and more aggressive range and also gain doubled HP (champion Hoppers will also have their HP doubled), a doubled jumping distance, and a faster movement speed. Putting out all Fireplaces in an area with Hoppers is a recommended strategy to stop them from turning into F. Hoppers.
Leapers strongly resemble Hoppers in advanced state of decay and bleeding at the neck, yet possess at least doubled health. They deal the same contact damage and typically hop around blindly, but seem to have a better sense of where the player is than Hoppers. What makes Leapers different from Hoppers is their ability to leap high into the air and land near the player's position, firing four blood projectiles in a cross pattern when they hit the ground. Possessing any powerup that allows flight - for example, Lord of the Pit or Transcendence - will allow Leapers to follow you and land onto ordinarily impassable terrain like pits and rocks as if it were normal ground.
Unlike Hoppers, they will not change forms when they touch fire and will take normal damage.