Hopper

A Hopper jumps around the room, doing contact damage to Isaac. They jump slowly around the room until Isaac gets close to them, at which point they start chasing Isaac. They can jump across rocks and gaps. If a Hopper touches fire (such as a fireplace), it becomes a Flaming Hopper.

Flaming Hopper
After touching a Fire Place, Hoppers will become Flaming Hoppers. Hoppers can also become Flaming Hoppers if they touch the fire spawned from or if they touch a Hot Bomb.

Flaming 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, Flaming Hoppers will follow Isaac within a much larger and more aggressive range and also gain increased HP, a doubled jumping distance, and a faster movement speed. Putting out all Fire Places in an area with Hoppers is a recommended strategy to stop them from turning into Flaming Hoppers.

Hoppers cannot become Flaming Hoppers by jumping into the fire created by the.

Flaming Hoppers will still take damage from the burning status effect.

Leaper
Leapers are similar to Hoppers, hopping around the room and chasing Isaac when he gets close. What makes Leapers different from Hoppers is their ability to leap high into the air and land in Isaac's position, firing four blood projectiles in the cardinal directions when they hit the ground.

Unlike Hoppers, they will not change forms when they touch a Fire Place and will take normal damage.

Sticky Leaper
Sticky Leapers are tar variants of Leapers that were added in The Binding of Isaac: Repentance.

Just like normal Leapers, they have the ability to leap high into the air and land in Isaac's position. When they land, they spawn black creep and spew several tar shots around themselves.

Eggy
Eggy is an enemy that was added in The Binding of Isaac: Repentance.

It behaves similarly to Hopper, jumping around the room and chasing Isaac, spawning white creep wherever it jumps. When it takes enough damage, it spawns a group of Swarm Spiders.

Tainted Hopper
Tainted Hoppers are much stronger and tankier versions of Hoppers. They jump and twirl around the room, shooting 4 rings of projectiles, each increasing in size compared to the last. The first shot has 4 bullets, the second has 6, the third has 8, and the last has 12.

They are exclusive to the Ascent to.

Trivia

 * Hoppers share similar movement patterns with Tektites from The Legend Of Zelda.