Weapon finesse is worded as an option. It says you “may” do something, which means you also may not. But feral grace won’t trigger without using weapon finesse.
When the animal companion makes a melee attack with the chosen natural attack using its Dexterity bonus on attack rolls and its Strength bonus on damage rolls,
If you aren’t using dexterity for the attack roll or aren’t using strength for the damage roll, then feral grace doesn’t do anything.
"If you aren’t using dexterity for the attack roll or aren’t using strength for the damage roll, then feral grace doesn’t do anything." If you are using Weapon Finesse, than Feral Grace still does almost nothing, because the feat is extremely weak. The progression is very slow (+1 damage each at 4th, 9th, 14th, and 20th level), and what's worse, it only affects one attack out of the three (five when pouncing) that a lion has. Even if you would want to use Weapon Finesse would Feral Grace be a bad choice.
If you really want to increase the lion's damage, Martial Focus is aviable at 8th level and adds +1 damage to all attacks; the feat also opens up the possibility of Cut from the Air or Difficult Swings.
An animal’s feat selection is pretty limited unless you first increase their intelligence to 3+. Otherwise they can only choose from a small selection of feats or feats made specifically for them.
Animal Feats
Animal companions can select from the following feats: Acrobatic, Agile Maneuvers, Armor Proficiency (light, medium, and heavy), Athletic, Blind-Fight, Combat Reflexes, Diehard, Dodge, Endurance, Great Fortitude, Improved Bull Rush, Improved Initiative, Improved Natural Armor, Improved Natural Attack, Improved Overrun, Intimidating Prowess, Iron Will, Lightning Reflexes, Mobility, Power Attack, Run, Skill Focus, Spring Attack, Stealthy, Toughness, Weapon Finesse, and Weapon Focus. Animal companions with an Intelligence of 3 or higher can select any feat they are physically capable of using. GMs might expand this list to include feats from other sources.
it only affects one attack out of the three (five when pouncing) that a lion has.
Only 1 if you choose bite. But if you chose claw, it’d work for 2 of your attacks. And rake attacks are also claw attacks, so it should work for those too, but check with your GM.
a monster with the rake ability gains two free claw attacks that it can use only against a grappled foe.
With pounce having text to allow you to use the claws then as well.
The feat isn’t the strongest, but it’s not bad. Pure dexterity to damage isn’t as good here, because the companion will have a fairly high strength score no matter what you pick. The problem is that the feat wasn’t intended for a strong companion. It’s meant for something more like a velociraptor.
I missed that, but you don’t even need int 3 to take feral grace. It’s a feat for animal companions and so allowed by default.
it only affects one attack out of the three (five when pouncing) that a lion has.Only 1 if you choose bite. But if you chose claw, it’d work for 2 of your attacks.
Based on the wording, you only pick on attack, not one 'form' or 'type' of natural attack. This FAQ makes a clear disinction between "one" and "one type".
Also compare the general natural attack rules: "If a creature has only one natural attack, it is always made using the creature’s full base attack bonus and adds 1-1/2 the creature’s Strength bonus on damage rolls. This increase does not apply if the creature has multiple attacks but only takes one. If a creature has only one type of attack, but has multiple attacks per round, that attack is treated as a primary attack, regardless of its type." Bestiary pg. 302Contrast the Improved Natural Attack feat, which makes you chose "one of the creature’s natural attack forms".