All familiars can attack and use one pre-determined command. They then have up to 4 other commands that you can allot “tricks” to. Tricks are special attacks and spell-like effects that familiars can use by spending their master’s MP (magic points).
Familiars learn new tricks at predetermined levels, but players can also teach them tricks by feeding them gems. Not every familiar can eat every gem; the elemental nature of the gem needs to agree with them.
But most familiars are able to eat a wide variety of gems. Gems are a great way to teach powerful abilities to lower-level familiars who would otherwise be useless in combat.
Gems can’t be purchased or made in the alchemy cauldron, but they are commonly found in treasure chests and as task rewards.
To use a trick in combat, it must first be placed in a command slot. Select the familiar from the Friends & Familiars menu and press i to open up the Commands option in order to allocate tricks into the command slots from its list of known tricks.
Familiars have a limited number of command slots in which to place their tricks. Initially, most familiars have only a single free command slot, but you can unlock three additional command slots via some combination of leveling them up in combat, raising their familiarity by giving them treats, and making them metamorphose.
Familiars can also only learn up to 8 tricks in their list of known tricks. If you want your familiar to learn a new trick once it reaches this limit, you must permanently replace one of its existing tricks in that list.
The specifics vary for each familiar, so see the Familiars chapter in the full guide for details..