I've used lots of information that Havard and The Glen (who I assume is Glen Welch) have published at Pandius or YouTube. In fact, when my players entered Darokin I just played the 10 minute video by Glen Welch and let the players listen to it while getting my stuff ready for the session.
Mystara benefits from fans really knowing the setting and with nothing published for two decades there's lots of fan material to pick and choose from to alter the game to your liking.
It's easy enough to take point #6 in Havard's post (a world where the strangest races feel right at home) to, for example, justify adding Tieflings and or Dragonborn.
Mystara was very additive and only rarely subtractive. It added all sorts of races, classes, nations, to the game. There's even the only example of fantasy Dutch I can recall. And it's a horrible pun as they are Followers of the Flame - Flaemish. So adding Tieflings or Dragonborn makes sense. There are even Diaboli that you could refluff as Tieflings if you wanted to.
The rare subtractive elements are justifying why half-elfs don't exist and why dwarves/halflings can't cast arcane magic, for example.
The setting also does a great job of mimicking 5e's Tiers of Play, which roughly follow the BECMI boxed sets. You see it in Havard's point #2 (Room for both low level exploration and plane hopping world altering epics.) The modules were forced to accommodate the boxed sets and the Gazetteers were forced to accommodate the modules. The result is that if I ever got a campaign to double digit levels I'd have tons of options based on the PCs' prior choices.
Mystara benefits from fans really knowing the setting and with nothing published for two decades there's lots of fan material to pick and choose from to alter the game to your liking.
It's easy enough to take point #6 in Havard's post (a world where the strangest races feel right at home) to, for example, justify adding Tieflings and or Dragonborn.
Mystara was very additive and only rarely subtractive. It added all sorts of races, classes, nations, to the game. There's even the only example of fantasy Dutch I can recall. And it's a horrible pun as they are Followers of the Flame - Flaemish. So adding Tieflings or Dragonborn makes sense. There are even Diaboli that you could refluff as Tieflings if you wanted to.
The rare subtractive elements are justifying why half-elfs don't exist and why dwarves/halflings can't cast arcane magic, for example.
The setting also does a great job of mimicking 5e's Tiers of Play, which roughly follow the BECMI boxed sets. You see it in Havard's point #2 (Room for both low level exploration and plane hopping world altering epics.) The modules were forced to accommodate the boxed sets and the Gazetteers were forced to accommodate the modules. The result is that if I ever got a campaign to double digit levels I'd have tons of options based on the PCs' prior choices.