Alter Egos are summmoned by casting Trust Magic.
Level and Attributes
The summoned alter ego’s level and attributes vary based upon the summoning player’s level and/or Item Level. For regular levels, alter egos do not level when the player does, so they have to be dismissed and resummoned to match. Item Level changes are reflected immediately, which can cause problems when using gear swap macros. Alter egos do not receive party bonuses.
Alter egos can enter the following battlefields, but must be summoned before entering the battlefield.
Quests: Beyond Infinity
- Reported by Square-Enix to have been implemented in February 2014: 
Rank 2 and Rank 5 Missions:
- Rank 2-3: The Emissary / The Three Kingdoms / Journey Abroad
- Rank 5-1: The Ruins of Fei'Yin / Darkness Rising / The Final Seal
- Rank 5-2: The Shadow Lord / Xarcabard, Land of Truths / The Shadow Awaits
Chains of Promathia Missions:
- 1-3: The Mothercrystals
- 2-5: Ancient Vows
- 3-5: Darkness Named
- 4-2: The Savage
- 5-2: Desires of Emptiness
- 5-3: Past Sins (Louverance's Path): A Century of Hardship
- 5-3: Where Messengers Gather (Ulmia's Path): Head Wind
- 5-3: Where Messengers Gather (Ulmia's Path): Flames for the Dead
- 6-4: One to be Feared
- 7-5: The Warrior's Path
- 8-3: When Angels Fall
- 8-4: Dawn
Treasures of Aht Urhgan Missions:
- The Black Coffin
- Since this battle takes place in a dungeon rather than a battlefield, alter egos can be summoned once onboard The Ashu Talif. They do not need to be summoned before zoning into the battle.
- Shield of Diplomacy
- Puppet in Peril
Seekers of Adoulin Missions:
- All Wildskeeper Reives
- All battles involving a Microcosmic Orb or Macrocosmic Orb
- Skirmishes in Rala Waterways (U), Cirdas Caverns (U), Yorcia Weald (U), and Outer Ra'Kaznar (U)
Alter Ego Restrictions
Locations Where Trust Magic Can Be Used
- Trust spells cannot be cast in cities, Dynamis, Abyssea, Limbus, Assault, Salvage, Meeble Burrows, and other areas where special battle content occurs (other than Reives, Campaign Battles, and certain battlefields; battlefield use is limited; see previous section).
- A message is displayed when attempting to call forth an alter ego in an invalid area.
Party and Alliance Restrictions
Players can now summon alter egos while in a party containing other players.
- The summoning must take place after the party is formed.
- If Level Sync is activated, all alter egos vanish and must be resummoned, so summon them after Level Syncing.
- Only the party leader is able to summon forth alter egos.
- This particular restriction is in place for the June 2014 version update in order to prevent a particular glitch.
- Alter egos cannot be summoned in the first 120 seconds after forming a party.
- Alliances cannot be formed when in a party comprised of bother players and alter egos.
- Parties cannot contain multiple alter egos of the same NPC.
Number of Simultaneously Summonable Alter Egos
- Up to three alter egos can be summoned at once.
- Unlike pets and fellows, alter egos are considered party members.
Using Alter Egos in Reives
- Alter egos may be summoned in colonization, lair, and wildskeeper reives, but they do not receive momentum bonuses.
Summoning Multiple Copies of the Same Alter Ego
- Only one alter ego of a given NPC may be summoned at a time.
Trust Spell Recast Time
- Each Trust spell has its own recast time, and hence a given alter ego may not be re-summoned until the requisite amount of time has passed.
Summoning Alter Egos in Combat
- Alter egos cannot be summoned while the player is already engaged in combat.
Dismissing Alter Egos
- Alter egos vanish upon logging out, changing zones, being charmed by a monster, or falling in battle.
- They may also be dismissed manually by selecting "Release" from the action command menu.
- Outside of battle, alter egos can be targeted and dismissed with the text command /refa (short for "Recall Faith")
- Outside of battle, all summoned alter egos can dismissed without targeting them using the text command /refa all