From LSWiki

Contents 1 Bonding Requirements 2 Known Abilities 2.1 Combat Bonuses 2.2 Attribute Modifications 2.3 Manipura Chakra 2.4 Specialty Bonuses 2.5 Charms 2.6 Combat maneuvers 2.7 Additional Bonuses and Powers

Bonding Requirements

Looks like empathy is the main requirement, based on the failure message:

You sense that the black male panda bear feels as though you could use more affection and warmth in your life.

(One was successfully bonded with a buffed empathy of 130 and not much else besides a couple of trains as a fresh human VV explorer)

Known Abilities

Combat Bonuses

Some amount of empathy, centering, and horticulture are applied to both attack rating and damage

Attribute Modifications

Manipura Chakra

Looks like Panda familiars open and charge the Manipura chakra periodically.

Specialty Bonuses

Bonus specialty degrees and access are provided as follows:

Charms

Shortly after bonding

• Standard Charms
• Tame
• Command

Somewhat frail

• Enable Darkvision

Combat maneuvers

• Around Fairly Healthy

Perform Stone Root Palm

Empathic Bonds Maneuver
Usage: perform stone root palm [into <target>]
Activity Cost For You: 28

Channel a rooted palm strike that carries a surge of earth-aspected force into a target.

Additional Bonuses and Powers

You can pet or hug your panda to receive the following message that probably does stuff.

You sense a gentle welling of comfort from your panda familiar.

Sometimes you will regenerate earth energies with the message

You feel the steady pulse of the earth underfoot seep into your bond, replenishing the earth within you.

Looks like this only happens if your bond is on the ground, so not while being carried.