Final Fantasy XIII - Gestalt Mode
Gestalt Mode is available after a Summon has appeared. You can activate this
after summoning by pressing the Square button. If you chain attacks with the
summon before activating Driving Mode, the Gauge will increase and thus make
Gestalt Mode last longer.
The controls are different when you change to Gestalt Mode. You use different
button combinations and left analog stick directions to perform special
abilities. Pressing X (PS3) or A (Xbox) will activate Auto Gestalt
which executes abilities automatically. The timer will decrease
each time an ability is used. The cost of each ability is shown to the left
of the ability. When the timer runs out, the summon disappears and any
chains and/or Stagger created are reset and the party members all restore
their HP and status ailments.
For more information I suggest reading the in-game Datalog as it provides
the info with pictures.