"Pairing Pokemon". I've had this idea based on the "Bonds" mentioned in the trailer, basically you could pair up two Pokemon in your party. They'd provide each other with a small stat boost, based on their base stats (like covering for the other's statistical weaknesses a bit?), and their could also be species-based "Support Abilities" that aid their partner when they're in battle. This would be mainly for Single Battles, though, not Double Battles where Pokemon already cover each other. As their Bonds grow, the stat boosts would grow too, and the Support Abilities would have better chance of activation.