Hi All!
I was able to get a Eurail pass for my upcoming trip for 20% off by purchasing it during a promotion for shoulder-season travel. Here's how I did it and what to keep in mind so that you can save money too.
The most important part is subscribing to Rail Europe's email list so that you know when promotions are being held, as they only last ~3 days. The link is https://www.raileurope.com/en-us/discover/train-ticket-special-offers, enter your email in the right corner. Once discounts are active, you can buy from either the Rail Europe or normal Eurail websites (at least, I was able to). Promotions are typically in early March, early July, and on Black Friday, though the email list ensures you won't have to remember this.
These promotions are a set amount, typically 15% or 20%, off of all passes. Great news, the discounts also layer on top of Youth (25% off) and Senior (10% off) discounts! The only qualifier is that you must start your pass before or after a certain date, but if you're already traveling shoulder season this is likely not an issue. For example, I was able to get a 10 days in 2 months pass for $308 (Youth + 20% off) as long as I begin use on or after September 1st. Bon Voyage!