What's the most important piece of advice you'd have for an undergrad student who wants to land an entry-level PMM job, despite the fact that a bulk of PMM jobs require an MBA?
The most important thing I can tell you is that your first job out of college won't define your career forever. So don't be afraid to take risks!
Several large companies have associate product marketing manager programs or rotational programs that you can apply for. Make sure you check when applications must be submitted, as the programs follow a biannual (I think) schedule.
With that said — generally, it's rare to start your career in product marketing because it’s often a more specialized role. So I recommend looking for roles that will help you learn about businesses, customers, and storytelling. Bonus points if you get the opportunity to work cross-functionally. I started my career at a small company (less than 30 people) doing marketing communications and operations. I spent over a year there as the only Marketer, meaning I had to wear many hats. The silver lining was that I learned how a business functions, how teams work together, and the importance of customers. That experience led me to my next role, then the next, and now to Product Marketing at Drift.
The point is: building (more) general skills early in your career will enable you to better define the path you want to take later on. So learn as much as possible in every role you're in. For example, if you're in an entry-level marketing role — take full advantage of understanding your marketing channels, how campaigns are developed, and how to track performance. All of that will come in handy, I promise.
Just remember, things don’t always work out as planned, but they work out as they should. This sounds cheesy, but I’ve come to appreciate this phrase.