Pack Instinct

Here are all the pack buffs you get with the new instinct types. Having more than one of the same pack type adds to your animal pack buff.

Pack Type Creatures
Arachnid Frost Spider, Giant Spider, Scorpion, Wolf Spider
Bear Black Bear, Brown Bear, Grizzly Bear, Polar Bear
Bull Bull
Canine Dire Wolf, Dog, Grey Wolf, Hell Hound, Timber Wolf, White Wolf
Daemon Fire Steed, Imp
Equine Fire Steed
Feline Cat, Cougar, Hellcat, Leader Hellcat, Panther, Predator Hellcat, Snow Leopard
Ostard Desert Ostard, Forest Ostard, Frenzied Ostard

As suggested above, a Frost Spider and a Giant Spider both belong to the Arachnid group and can be used together to receive the pack instinct damage bonus. However, while a Frost Spider and Black Bear both can use pack instinct, they do not receive the damage bonus when used together since one is of the Arachnid group and the other is of the Bear group.

Pets in Pack Damage Bonus
2 +25%
3 +50%
4 +75%
5 +100%