Use the various Chaosium and Mongoose texts as you see fit. But for the record this is what I would use:
- any edition of Call of Cthulhu, with the monsters, modern weapons, spells and so forth.
- Demon creation rules from the edition of Stormbringer you can get your hands on.
- Optionally, spells from the Bronze Grimoire, though it’s more for colour than anything eles. Mix them in with the other CoC spells which, as previously noted, are forbidden.
- CoC‘s Dreamlands. I like that there’s a Moorcockian treatment of dreams as well, but I confess to preferring the Lovecraftian one. It’s weirder.
Originally in Runequest some skill percentages of were considered adequate at 30% or so (languages, for example). Unfortunately not all skills are created equal; a 30% skill for the most part does not indicate competence. Even if the GM says “hey, don’t bother rolling, your skill is good enough” it jarrs with the character’s perception of their PC — which should be of a capable individual the player can have confidence in (otherwise, why attempt anything, ever?).
For BRP-style systems I like to consider skills well in excess of 100%, and call that the base level of “expertise”. A pass for a skill is rolling equal to that number or less; a success, however, is rolling under half the skill. Now, the ideal range for percentiles in a challenging system is between 30 and 70%. Any less than 30% is really no chance, and any more than 70% is a walkover. With the pass/success granularity you can start making base skills above 50% for novices, which means the players can at least have some confidence in their character. Additionally equating a skill level of 100% to expertise seems right; experts will make routine tasks seem trivially easy.
Other levels can be added — this is what I like to use:
- Roll under the skill % — Pass
- Roll under 1/2 skill % — Success
- Roll under 1/5 skill % — Extra Success
- Roll under 1/20 skill % — Critical
…and so on. You could add another level of granularity at say 1/10 skill if you really wanted, but I wouldn’t bother — for someone with 100% skill the difference between Pass and Success is 50%, between Success and Extra Success is 30%, and between Extra and Critical is 15%.
If you want to get really creative you could consider “Super Crits” of 1/50 or even 1/100 of the skill — but those should only come into play when absurdly high percentages are reached (say 300%).
In combat splitting the percentage is an option, and this starts to be a tactical decision at high percentages. Should you split the % for multiple Passes, or should you roll fewer times to get Successes?
(for combat I’ve usually considered a Pass to function at half the effectiveness of a Success for parries, e.g. halving the AP of the parrying weapon).
Of course, what did for the Melniboneans’ global Bright Empire was a big war with the Dharzi. Crucially this came long before Elric’s time, and is given as a reason for humans taking hold of the world as Melnibone retreated to the Dragon Isle to lick its wounds. This makes the Dharzi hardly relevant — certainly they have no role to play in the 1920s society. They do have a role as an ancient enemy of Melnibone, and could feature in myth as another component of the broader Mythos.
There is the option to make the Dharzi appear here and now. In doing so you’re lifting events from long before Elric’s time and inserting them well after the end of his life (after he blows the Horn of Fate), but it would work. Dharzi came from the “unknown East” which in this game could be Asia, with opportunities for tie-ins with the Plateau of Leng and other mysterious places in the Mythos.
This would lead your campaign in a couple of directions. Firstly you will probably diverge from Earth history, which is fine if that’s what you want. Second, your game may turn into a war game, which could also be fun but not the same as an investigation game.
A third consideration: if the Dharzi emerge now, does this change the relationship of people with natural forces and beasts? Dharzi were “beast worshippers”. On the other hand Melniboneans already had ancient relationships with the Beast Lords and Elemental Rulers, so the lack of Dharzi in the history of your game world probably won’t upset the metaphysic.