Who is/was Sardon the Beige?
Sardon the Beige is a human wizard who resides in the city of Everteeter. He may or may not appear in the future (faster on my site, wink wink, plug plug), but I will say this: he is considered a great hero (a “gosh”, as Brudil would say), but he is getting on in years and is often visibly tired. If one didn’t know about his mighty deeds, he’d likely be called “lazy” and “reclusive”.
In the world of Dungeon Smalls, is it common for gnomes to go 'adventuring'? Or for goblins to learn magic?
For gnomes, it’s more common to see one only taking on dangerous jobs when necessary. While they are generally one of the more resilient folks around, they tend towards aiding their local community with remarkable persistence. A more common adventure is either a rescue mission or gathering resources from a place that’s dangerous for other folk due to things like poor air quality.
As for goblins, it varies. Goblins in general believe each one of them has a destined ambition (often referred to as “Paubb’s Call” after the god of action). They may not be the best at their passion, but you can reliably guess they will strive for improvement at every turn.
So while anyone could feasibly learn magic, if a goblin feels Paubb’s Call pulling them to spellcasting, they WILL learn it.