Dople

A Dople is a completely skinless Isaac-like monster that can be encountered in Chapter 4. Doples mirror Isaac's movements exactly. They attack by firing blood shots, but only when Isaac fires tears, and these shots are fired at the same frequency as Isaac's tears.

Evil Twin
Evil Twins look like Doples that are black and have horns and wings. They shoot three spread blood shots instead of one but have a reduced fire rate. Also, due to the fact that they have flight, they cannot be hurt by spikes.

Trivia

 * Evil Twins appear to have ability, given the fact that it has a spread of 3 shots and a slower fire rate compared to Doples.
 * Doples and Evil Twins are based on the term doppelganger, which means a double of a living person.
 * Doples are a reference to Doppelgängers from the game Tomb Raider. It's a replica of Lara Croft, the protagonist of the video game, and can be found in The Great Pyramid. It's a skinless creature that would mirror the player's movements and could be tricked into jumping into a pit of molten lava.