Poke ball is a technique a Pokemon begins with in Slash'EM Extended. Players of ungenomold race also start with it, and it can be randomly learned by a zyborg on leveling up. If a binder advances their whip skill to expert, they will also learn this technique.
Using this technique causes the player character to throw a poke ball at an adjacent monster, taming it if successful, or moving on to the next adjacent monster if not; that means, if the player is completely surrounded by monsters on all sides, the ball can catch any of those monsters. Only one monster may be caught per ball, though, and regardless of the ball actually catching something or not, the technique will then have a random timeout of about 1000 turns before it can be used again.
If the monster is unique or a quest nemesis, it cannot be caught. A monster flagged as "petty" will always be caught if the ball is thrown at it. Other monsters can only be caught if their level isn't higher than the technique's level, and if that is the case, there is a random chance of the ball actually catching it; the chance is higher if the technique's level is higher, and lower if the monster's level is higher. An exception is made for monsters that represent actual Pokemon, like gyarados or rhyhorn: there's a chance to catch them even if the player's level is lower than theirs, and the chance of success is higher than it is for other creatures.