Hey! I actually did my HSF Summer Vac AC recently (first-ever AC!) and was accepted later the same day
Top tips would be to prepare your why law, why hsf, an example of teamwork, an example of failure - these are key ones but the rest flows more or less like a conversation around what you answer. As far as the scenario-based interviews, it's true that these are super hard to prepare for! Gain an understanding of M&A, JVs, how banks assess borrowers, types of investors and just your commercial awareness in general. I am a non-law student though so if you're a law student you may get more technical questions - hope that helps!