My buddy has a '97 Tracer and is starting to get into modding and got an intake but when he removed the stock intake, he said there is some sensor that he would have to take off. I have been doing intakes for a little while now but never came across a sensor on/in the intake. Could he just take it off?

most small engines have the air flow sensor on the intake (which is why aftermarket intakes usually have holes for reinstalling the sensor). You can remove it from the old intake, but you must reinstall it in the new intake for the engine to work properly.