Aside from the fact that both of these are martial classes, there isn’t a ton of inherent mechanical synergy here. The adept class runs primarily on Dexterity and Wisdom, prefers no armor or light armor (depending on the defensive option selected) and the marshal class tends toward Strength and Charisma with heavy armor. Flavor-wise, there’s a bit more to work with. From the archetypal Japanese dojo to European-style fencing schools, there’s definitely room for a character that acts as a trainer and leader of those who study advanced combat techniques. In addition, both classes, while not quite blank slates, definitely have a lot of room for customization and different flavor. In play, you’re probably going to want to pick whether to emphasize your adept or marshal levels relatively early one; emphasizing the former will give you a mobile, athletic skirmisher with some leadership skills they can use when the opportunity presents itself, and more levels of marshal gives you a strong battlefield leader with a bit of extra speed. A roughly even mix allows you to make the “great master” character that is both a leader and a formidable combatant in their own right, though perhaps not as good at either as someone who truly focused on one or the other. [[Synergy Feats for Multiclassers#Adept w/ Marshal|Adept-Marshal chains and ideas]]