My GM is running RMSS, which is close enough to RMFRP that most of that version of ERA works nicely. There are a few things that are different, however, plus I have a homebrew Profession with its own spell lists to work with. Here are the things that are giving me trouble so far:
1: In RMSS, you can take spells from lists outside your own Realm, and non-magic-user classes choose a Realm at character creation, which makes that one slightly easier to learn in. Buying spells outside your own Realm is exorbitantly expensive, but we have a player who did, so I have to make it work. As spell lists don't seem to list their Realms or whether they are Open or Closed (at least in the examples), I am not sure how to even begin to go about this. I figured out I could probably add the Realm-specific Groups to that config file, which would allow me to assign costs, but what do I need to do to designate a spell list as, for example, an Essence list? Or do we just do that by which Group we choose when we add it?
2: The way Stat changes upon leveling work is apparently completely different than RMFRP. In RMSS, you roll 2d10, and whether you get doubles and the exact roll determines if your Stat goes up or down and by how much. There is no other way to adjust them up or down (no option to spend DP on them). As there is no DP cost, I guess we can just manually adjust the stats after rolling in real life, but it would be nice if there was a way to track it in ERA.
3: When adding Development Packs, I found the place to indicate the name of the pack and how much it cost in DP, but it doesn't seem to have any mechanical effect, and if I add the skill changes manually, they (for obvious reasons) are included in the DP expenditure on top of the cost of the pack itself. I assume I am doing this wrong, but I can't find any reference on how to do it correctly.
4: Everyman/Restricted/Occupational doesn't seem to work the way my GM was expecting. His expectation is that it would be marked e/r/o, and would modify the number of ranks acquired- buy one, get two, for example, with Everyman. No option to buy just one rank with Everyman or Occupational skills, no way to save up to buy a rank with Restricted skills. I have just tested with "additional ranks" and it still looks odd on the sheet and I can't tell for sure if it is working correctly for his expectations.
5: The homebrew Profession, Soothsayer, has custom spell lists, so the first item also affects knowing how to designate some lists as the Base lists for Soothsayer, both for listing and for cost. In the Magician example, I see some lists entered as Favorites, but I don't see how they are designated as Base lists.
6: Soothsayer's lists include the Learn Language tree, which has an Everyman-like effect on learning new languages while the skill is active. For our game's purposes, the GM is applying it as a modifier at leveling unless there is some situation where a new language appears at a time when the character can't afford to be using magic for whatever reason. This means the number of ranks grated per rank purchased varies over the course of the character's growth. Even more, at higher levels, the multiplier goes up as the spell level does, and the player with the homebrew character is currently at a modifier of 3, and about to go up to 4. I can kind of jigger 3 with marking it as Occupational, but i have no idea how to handle 4 and up.
Thankfully not relevant for our game, but this spell line isn't the only reason this could matter- the Sailor Development Package (I think, could have been Mariner) modifies certain skill costs, but only when you stay involved with the sea. Go inland for too long, and the skills revert to their previous costs.
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I think that's all I have run into so far. Current plan is to build what I can of Soothsayer, a Group for spell lists outside of the Realms of professions currently in use, and the homebrew spell lists, and wait on answers to the above, or more issues to crop up. Hoping most of these are just me not noticing the right places to poke, since that's the easiest to fix.