The regulator is the ability that lets the user control pressure exerted on fluid or gas as well amount of liquid or gas is allowed to flow. For Eg, someone has a quirk regulator he can control the amount of gas or liquid that can flow around him not only that it can increase or decrease pressure exerted on gas and water or by gas and water. For Eg person who can travel below the surface of the ocean without being crushed if he has enough control over his quirk. He can regulate the flow of gases to produce more powerful wind attacks. He can also counter any fluid-based attack like from midnight. By increase pressure in the air around people, it can also make it hard for people to breathe like happen in the mountain when people reach a certain height they start having trouble while breathing. He can control the speed at which gases or fluid travel by adjusting the flow.
The regulator is a great and versatile quirk as not only it's allowed to control the pressure exerted on fluid or gases but also control the flow of fluid or gases. Thus gave the user to manipulate blood flow within his body as well as other body. The range of his quirk can be improved with more practice.