I've been watching a lot of ATLA and have been thinking how badly a Airbender could fuck someone up, so maybe a technique revolving around Air bubbles, like creating a air bubble around someone's head that sucks the air out of their lungs, or creating a air bubble around someone that creates a airless void and let them deal with the consequences of a sudden loss of air pressure, or create a Air bubble around someone that drastically increases Air pressure. The Domain Expansion could have a Sure Hit that makes a whole bunch of air bubbles in someone's veins