Gish

Gish is the protagonist of the game. He is a ball of tar, who's been living happily with his human girlfriend Brea until she was kidnapped and taken underground. Now Gish has to go after and save her.

Gameplay
Being a ball of tar, Gish has some interesting abilities to help him make his way through the levels. Of course, there's simple movement, too. Besides, Gish has 4 basic abilities and a secret one:

Becoming sticky
That's an ability you're going to be using a lot. In sticky-mode Gish can crawl around the walls or the ceiling, stick himself to solid blocks, grab and move loose objects. Also, if you repeatedly tap the stick key, you can gain some additional speed.

Becoming slick
While slick, Gish can go through narrow spaces, such as the 1 block wide tunnels. Also, being slick also seems to make him more resistable to being crashed. When used with sticky-mode, slickness will prevent Gish from sticking to loose objects.

Becoming heavy
This ability is good for crashing enemies and breakable blocks. Also, this ability is useful for throwing blocks. You just have to put a block you need to throw on top of you and become heavy, making Gish launch the block in the air. Being both slick and heavy allows you to speed up on downward ramps.

Jumping
Gish can jump, too. To jump, he first needs to compress himself, and then press the jump key to extend, launching himself in the air. The more Gish compresses himself, the higher he jumps.

Telekinesis
This is a very secret ability. To unlock it, first you have to go all the way to stage 5-1. There are some shortcuts, though you'll still have to complete some levels. On the stage 5-1 there's a secret place. To access it, you have to jump from the swinging platform on the start on the ledge left above. Then, in the ceiling, a secret tunnel can be found. It leads in a small room with a question mark. To unlock telekinesis, you have to touch the box, which is actually the point of the question mark. After that Gish becomes transparent, and now you can use your mouse to move loose objects.

Trivia

 * Gish was later added to The Binding of Isaac as a boss and, subsequently, The Binding of Isaac: Rebirth.
 * He was also made into the familiar Little Gish once defeated.
 * Gish has also appeared as a character customization in another one of Ed's games, HOST.