Feral Link

a gameplay element The Feral Link, also known as Synchro Drive in Japan, is a gameplay element appearing in Final Fantasy XIII-2. It allows the player to execute any recruited enemy's special attack, thus dealing a significantly larger amount of damage than normal, by correctly performing the necessary actions required by a triggered Cinematic Action.

Datalog
You've obtained monster crystals!

In this demo, a chocobo, Caith Sith and flanbanero will accompany you on your journey.

''During Battle, press to perform Paradigm Shifts and summon your monsters. When the gauge in the lower left hand corner fills up, press to unleash their special attacks!''

Mechanics
When the Feral Link gauge fully charges, the player can press on the PS3 controller or X on the Xbox 360 controller to execute enemy's special ability. In IGN's "Quest for Lightning" trailer a new feature is added to support Feral Link system under the name "Synchronization". It is presumed that perfect triggering of the ability raises Synchronization which also raises skill's damage.

Trivia

 * Some enemies fighting alongside Serah and Noel have different names than when they are opponents. This may be due to the fact that, as mentioned in the PAX 2011 interview, you could customize these monsters in some way.
 * While performing a Feral Link, a distortion similar to one seen in Final Fantasy XIII during Full ATB Skill execution, is featured, although in a different angle. It probably means that these are the only unique abilities available to the player.