Use the Oath Stone of Orkos in Combat 10 Times
You will receive the Oath Stone of Orkos from Orkos at the end of Chapter 20, right after you defeat the Fury sisters for the Bros before Foes trophy. To use the stone in combat you must get really close to an enemy and press +. Try to do it when the enemies are grouped in order to maximize the number of hits for the Tag Teamed trophy.

You can decrease the cooldown and increase the duration of the skill by leveling it up with 5000 orbs. Considering how strong it is, especially in tandem with the Amulet, the upgrade is worth every last orb. Continue to use the stone until both Hello Friend and Tag Teamed unlock.

It should be noted that the stone can't be used on a number of bosses and occasionally airborne enemies. It also cannot be used on an invulnerable target such as a Cerberus in its bubble, or a Talos during its immune state. Lastly, using it too close to a target afflicted by the upgraded Amulet of Uroborus will cause your copy to instantly disappear rather than attack, while still putting it on cooldown.