Final Fantasy III is the first game in the series to feature Summons: Beasts that the party can call upon to aid them in battle. Summons would take on many forms in the FF series, having a god-like presence, the flashiest of moves and mechanics that can make them feel like fellow (if temporary) party members.
Despite being comparatively simple, FF3's system is a bit more complex than some of those that came after. Each Summon has three different skills to them: A White Magic effect, a Black Magic effect and a unique attack. Despite the label, the terms "White Magic" and "Black Magic" are a bit misleading: The "White" Effect is usually a form of buff to the party or status to the enemies while the Black Effect is usually direct damage. The catch is that which effect you get is decided entirely at random. The White and Magic attacks can be used by Evokers, while the Unique attack is used by Summoners; Whether Sages get all three effects or just the Evoker's effects depends on whether you're playing the 2D version or not.
Escape is the Level 1 summon and something of a joke summon. Escape summons a Chocobo rather than any of the giant beasts and one of the two Evoker options equates to doing nothing. Its abilities are:
This ability allows the party to flee from battle. It's useful for escaping a fight and not dealing with III's punishing run away mechanics, but obviously not very good for fights you actually want to have or can't run away from.
A joke effect: The Chocobo attempts to kick the opponent. As the question mark indicates, the effect will always fail.
Chocobo Kick except it doesn't fail this time. Unfortunately, the attack power is pretty low for where you get it, so the primary saving grace becomes its surplus of casts.
Icen is the level 2 summon. It is Shiva's summon and the first to have a Status White Magic effect. As a general rule, these are useful in the Famicom version as they have a guarenteed hit rate, but are much more of a gamble in the remake due to the rates getting nerfed. Keep in mind that bosses are generally immune or heavily resistant to "skip turn" statuses or Instant-Kill moves.
For this ability, Shiva puts the enemies to sleep. This can be good for buying time for the party to heal or buff.
Shiva attacks the enemy with an ice attack.
Shiva hits all enemies with an ice attack.
Spark is Ramuh's spell and occupies spell slot #3. Ramuh kind of gets the short end of the stick, as he doesn't have anything particularly notable as far as summons go. He's basically "Shiva but lightning".
Ramuh paralyzes the enemies. Much like Shiva, this can be good to get a grace period or to lower their numbers.
Heatra represents Ifrit and is a 4th level spell. Ifrit is one of the more useful Evoker summons because both of his effects are useful and hard to waste.
Ifrit heals the entire party. The healing factor is rather effective, making it a decent move.
Ifrit attacks one of the enemies with a fire attack.
Spell tier #5 belongs to Titan. Titan is unique in that every effect that he has is some form of attack. This means that if you want guarenteed damage and the enemy doesn't resist/isn't immune to Eath, Titan is your man.
Catastro is the first of the "Boss" summons, which require the Warriors of Light to fight bosses in order to receive them. In the case of Catastro, Odin must be defeated in order to get the summon ability.
Bahamur is the final summon spell and occupies the eighth spell slot. As the name implies, it is based on Bahamut and requires the player best the Dragonking in battle before they can use it.