Classic Enemies
The long-running "Final Fantasy" series features a large number of recurring monsters in various games. Chocobos are the iconic ride-able giant bird found in nearly every "Final Fantasy" title ever made. Also returning are bombs, which are large, floating spell-casters that, upon reaching low health, detonate and cause heavy damage to your troops. The obnoxious malboros are tentacled monsters that inflict crippling status effects upon your troops. Finally, the monstrous behemoths tear your army to shreds with their giant fangs and claws.
Undead
The mindless undead ghosts and skeletons attack you throughout the game. Unlike normal enemies, these undead take damage from healing spells and instantly die when struck by the Arise spell. On the other hand, both monster types are immune to spells and weapons that drain health; in fact, these effects work in reverse, healing the undead and damaging the attacker. Undead are also notoriously difficult to remove from the battlefield, as each ghost and skeleton has a chance to return to fighting form a short time after being defeated.
Easy Monsters
The simple goblins are commonly found throughout the game. Easily defeated, these monsters do battle with weak abilities and average statistics. Panthers generally offer about the same challenge, although at high levels they may sometimes inflict the "vampire" status on your troops. The living trees known as treants only appear late in the game and protect their fellow monsters with powerful defensive spells, but are easy to target and kill before they can cause trouble. Lastly, the fast but easy to dispatch pigs appear infrequently and make little impact.
Advanced Monsters
The disturbing octopus-wizards known as mindflayers can cause you to lose control of some of your characters with the "berserk" and "confuse" status effects, in addition to removing any positive buffs you may have cast on them. Ahrimans, better known as beholders, can completely disable or kill your soldiers using various status effects and the ticking time-bomb spell "doom." The speedy and highly dangerous aevis birds, unlike their more docile chocobo cousins, can at high levels turn your best troops into stone in the middle of battle.
Massive Monsters
Prepare for a heavy onslaught when facing the enormous half-man, half-bull minotaurs. Though combat with a minotaur is relatively simple, they will make short work of your low defense units if you allow the monsters to reach them. Around the end of the game, you will encounter powerful dragons, the classic flying and fire-breathing monsters that unleash heavy magic damage on your troops. Lastly, the multi-headed hydras make dragons look like harmless little lizards by comparison, destroying your army with massive area of effect spells in the "Midlight's Deep" mission near the end of the game.