Oob

The Oob is a strong enemy encountered in later chapters. It has a similar AI to Famine. When Isaac is not horizontal to it, it spawns Brains. When Isaac is horizontal to it, It does a very fast charge that covers the room once.

Tactics

 * Because Oobs are quite potentially powerful, the maximum number of Oobs that can appear in a single layout is usually only 2 to prevent over-difficulty.
 * Unlike Famine, Oobs and Black Maws can't be tricked into killing their spawn and both constantly hover towards the player.
 * It's ideal to lure Oobs over obstacles as they will then be unable to summon enemies due to the lack of spawn space beneath.
 * Though they may still attempt to do so which will just leave them immobile and vulnerable.
 * Because of their high HP and ability to spawn friendly monsters, Oobs are a prime candidate for.
 * Note that there is no limit on how many Brains the Oob can spawn at once. Meaning that if he is allowed to spawn too many it may result in the game crashing.

Black Maw
The Black Maw is a more demonic version of the Oob. When Isaac is not horizontal to it, it may spawn Leeches. When Isaac is horizontal to it, it very quickly charges to his direction and then doubles back, charging back to its original position. It explodes upon death.

Tactics

 * Black Maws tend to spawn along with other enemies but due to their lower health and death explosions, they can be used to clear rooms quickly if the player kills them in time.
 * Black Maws are a lot quicker at spawning enemies than Oobs so greater caution is advised.
 * A special ability they sometimes showcase in long horizontal rooms is to double-back after traveling at a random distance rather than having to fly out of the room first, this can also happen in contact with another enemy. Because of this, it's recommended to stay out of horizontal lining with a charging Black Maw even when he appears to be charging away.
 * Unlike the Oob, Black Maws can still summon Leeches regardless of whether they are over an obstruction or not, due to the fact that Leeches can fly.

Trivia

 * Oob and Black Maw are both enemies from one of Edmund McMillen's previous games Super Meat Boy.
 * Oobs and Black Maws are the only non-boss enemies that can charge off-screen.
 * Black Maws specifically are also the only monsters that double back after charging off-screen, making them unique.
 * Rerolling Gaping Maws with always turns them into Oobs.
 * Black Maws look surprisingly similar to the xenomorph's mouths from the Alien movies, but this could also be a coincidence.
 * It also slightly resembles a sperm cell.
 * Oobs have the highest health of any non-boss enemy.