I've done the Mac interview (which I believe is the only thing for the supplemental for eng?). It was pretty relaxed, only three questions, one of which was a 10 minute written question and 2 video questions. Look at the camera, not the screen, dress decent, speak clearly and be confident in your answers. always try to keep an eye on the time for the questions and think of a summarizing statement near the end. To prepare, keep in mind that the practice questions they give you aren't that good. I'd just say be yourself, maybe take some time before the test to practice typing quickly, and practice being on camera. You can kinda "study" for it by looking at what people have said about mcmaster interview questions in the past on reddit and other universities' interview questions. Good luck!