Each monster comes with a unique ability which you can release upon filling the Feral Link gauge, which is located below the monster's HP gauge. When the gauge is full, you can press Square to unleash the monster's unique ability. Each such ability comes with a QTE button input - complete it as quickly as you can in order to get a big Synchronisation Boost, which increases the effectiveness of the skill.
Whenever you kill a monster, there's a chance that you'll obtain its crystal (not all monsters can be captured). Getting the monster's crystal adds the monster to your menagerie.
There are four things you can do in the Monster menu:
add decorative items to the monster (serves no purpose whatsoever)
rename the monster (serves no purpose as well)
infuse the monster with other monsters (this is what I'm talking about)
release the monster
You'll likely spend a lot of time in the Infusion submenu, trying to make that perfect monster. Let me give you an example of how you can improve your favourite monster.
You have a lv40 Flanitor, MED, 4000 HP, 250 MAG.
You want to increase Flanitor's HP.
Go to Flanitor's Infusion submenu and look for a monster with passive ability HP+15% or similar.
Infuse Flanitor with the selected monster and Flanitor's HP will increase.
A monster learns battle/passive abilities as you level up its Crystarium by having the monster reach a certain level. For example, the monster gets HP+10% passive ability upon reaching lv10, and can cast Haste upon reaching lv20.
A single monster can have up to 10 passive abilities at any given time.
Paradigm Pack Tutorial
Upon entering the Paradigm Pack menu, you're greeted with the following choices:
Paradigm Pack allows you to add captured monsters to one of the three slots.
Customize allows you create paradigms as you see fit by choosing roles for Serah and Noel. Monster can only have one role, and it cannot be changed. Pressing Square on your chosen paradigm will make it a default paradigm, meaning that you begin the battles with that paradigm. Pressing Triangle allows you to save your paradigm selections in one of three slots (which can later be loaded via Triangle again).*1
-3rd allows you to auto-create paradigms based on preference of attacking power, defensive positioning or well-balanced.
- 4th allows you to delete paradigms (default paradigm cannot be deleted).
*1 note: By choosing the Tune option you can select how your party members behave in the chosen paradigm. 'Normal' means that characters will behave according to the nature of their selected roles. 'Cross' prioritizes actions that affect single targets. 'Wide' prioritizes actions that have area effects. It's up to you to decide.