Mount Feats

[Zeth Ryon]

So i get a lion to mount, it has 3 feats already,
im a 6 lvl cavalier, which means that my mount has access to 3 feats.

Those feats must be those that the Lion already has?
Can i change those 3 feats the lion already has?
Does it adds 3 new feats that i can chose?

It goes like this, but sounds stupid cause i can't change anything then.

Under the animal companions table:

Feats

This is the total number of feats possessed by an animal companion.

[Whale_Cancer]

How does the lion already have 3 feats? Animal companion lions are not the same as bestiary lions.

[Michael Sayre]

So, as an initial clarification, Animal Companions have nothing to do with their Bestiary counter-parts. You'd build it using the Big Cat entry from the druid Animal Companion entry with the appropriate adjustments from there.
So you start with:
Cat, Big (Lion, Tiger)
Starting Statistics: Size Medium; Speed 40 ft.; AC +1 natural armor; Attack bite (1d6), 2 claws (1d4); Ability Scores Str 13, Dex 17, Con 13, Int 2, Wis 15, Cha 10; Special Attacks rake (1d4); Special Qualities low-light vision, scent.

7th-Level Advancement: Size Large; AC +2 natural armor; Attack bite (1d8), 2 claws (1d6); Ability Scores Str +8, Dex –2, Con +4; Special Attacks grab, pounce, rake (1d6) .

And then apply the appropriate adjustments for a 6th level animal companion.

[Zeth Ryon]

I dinnae know that.
Okey, so Medium? Ican´t ride it if im medium too...

Is there any feat that would allow me to stack lvls from other clases
for the efective druid animal companion lvl?

Edit: Found it

Boon Companion
Your bond with your animal companion or familiar is unusually close.

Prerequisites: Animal companion or familiar class ability.

Benefit: The abilities of your animal companion or familiar are calculated as though your class were four levels higher, to a maximum bonus equal to your character level*. If you have more than one animal companion or familiar, choose one to receive this benefit. If you lose or dismiss an animal companion or familiar, you may apply this feat to the replacement creature.

Special: You may select this feat more than once. The effects do not stack. Each time you take the feat, it applies to a different animal companion or familiar.