Not to be confused with Marlboro (cigarettes), monsters called Malboro have been appearing in the Final Fantasy series ever since Final Fantasy VI was released (During Final Fantasy VI, it had the names "Oscar" and "Mad Oscar").
The Malboro is green in appearance, except for the Big Malboro (Final Fantasy Tactics Advance), which is purple. It is approximately two to three times the size of the player-controlled characters, and covered with tentacles. Also dead center in the middle of the Malboro's giant oval head is a mouth that stretches from one side of the head to the other. Inside the mouth are a large collection of giant fangs. Around the head are a bunch of smaller tentacles, each with an eye on the end.
The teeth are never used. Sometimes it attacks with its tentacles (FFTA) or it spits up dangerous acids. However, the one thing to fear in a Malboro is its Bad Breath. This attack hits all of the player's party with almost every status effect. In Final Fantasy VIII, the Malboro was one of the hardest monsters to beat, due to its scripting to use Bad Breath as the very first thing in the battle, before anything else happened.
Equipping a Ribbon (Nulls all status effects) usually assists greatly in defeating Malboros.