I am exploring an idea to do with Small Gods. I’m considering having them form covenants, agreements of exchange, rather than simply grant spells as normal gods do for clerics.

On the one hand, this opens the door to having non-clerics have access to powers from small gods (which is ideal, exactly what I want). In D&D 3.x and Pathfinder this is fairly easy to manage from a character build resource point of view, simply make them feats.

For OSR-style games, though… what are suitable build resources to use? Simple experience point cost is probably unhelpful because of how experience point costs for levels change so fast (typically doubling; 1000 XP at first level is somewhere between really big and immense for almost all first-level characters, but fifth-level characters might hardly notice). An experience point surcharge (‘penalty’ is the wrong word here) might be better for abilities that scale well with level.

With d20-based D&D you might also use something like prestige (or better, ‘paragon’) classes, where you advance “covenant level” or something, but first, I don’t particularly like that mechanism, and second, in OSR games I don’t know that you can readily ‘mix in’ other classes readily.

Perhaps treat them something like (non-physical) magic items? You have to earn them (you can’t simply ‘buy them’ by providing gold, you have to do something to get them), they do something for you that may be fairly tightly constrained in applicability, and if you break the covenant, your agreement with the small god who is your patron, they go away.

I think I have an approach now, prompted by conversation online. Mongoose Press’ Classic Play: Book of Immortals addresses this very thing with the rules for covenants.

Classic Play: Book of Immortals Covenants

In Classic Play: Book of Immortals it is possible to gain the patronage of a more powerful entity (where ‘entity’ isn’t necessarily a god, it could be a collective such as the Unseelie Court or the nation of Thaslabad). Once you gain the attention of the entity it may be possible to negotiate a deal, a covenant, whereby you gain something in exchange for service.

Service is almost ideal for my purposes, and can be scaled to my purpose and the benefits gained from a small god. Rather than trade character build resources, pull it up in play from time to time. Unlike Book of Immortals the covenants don’t have to grant steps toward apotheosis, they can be limited to more mortal concerns, but the structure itself covers a pretty broad range of costs.

There are several kinds of service identified. I will include below a brief description of each type of service (taken directly from the book).

• Allegiance: When an Immortal agrees to abide by an allegiance term  in  a  covenant  he  accepts  that  other  beings have the ability, if they follow the proper rituals, to command his time. The covenant must specify what beings can demand the character’s attention and what steps they must follow in order to do so.
• Bond: When an Immortal agrees to abide by a bond he agrees to do everything in his power to foster a specific set of  conditions  in  the  world.   These  conditions  will usually  favour  the  granting  power  in  some  way. However, they may also relate to expanding the role of one of the four mythic powers or to furthering the processes embodied by the abstract powers
• Commitment: The Immortal commits to the performance of specific practical  duties  on  behalf  of  the  granting  power. These duties require at least 10% of the character’s time.   The  duty  always  involves  some  physical  or magical action. Most duties involve something the granting  power would  have  to do  anyway  or needs done by a third party for some metaphysical reason.
• Nemesis: When  an  Immortal  agrees  to  take  on  a  nemesis  he dedicates himself to the destruction and humiliation of  a  particular  opponent,  race  or  people.   He  must do  everything  in  his  power  to  bring  his  foes  low, even sacrificing himself if it is required of him. The granting power will bind the Immortal to a nemesis that opposes its goals; it may even be a former friend or colleague from the Immortal’s mortal days.
• Offering: The  Immortal  agrees  to  make  regular  offerings  of a  material,  magical  and  metaphysical  nature  to  the greater glory of the granting power. The Immortal makes  offerings  in  public  and  in  private.   Public offerings must be remarkable, impressive and flashy enough  to  attract  attention.   Private  offerings  must involve  deep  personal  sacrifice,  to  the  point  where giving up the offering actively pains the character.
• Quest: When an Immortal agrees to undertake quests as part of a covenant he must immediately undertake an epic quest in addition to the challenge he just completed. Once  he  completes  this  quest  the  granting  power may,  at  its  option,  call  upon  the  hero  to  perform  a similar quest every decade. These secondary quests do not count as challenges for the Immortal, although they may aid or oppose challenges taken by others.
• Ritual: The  Immortal  agrees  to  enact  specific,  meaningful actions  at  specific  times  each  year.   These  actions relate  in  some  fashion  to  either  the  world’s  mythic history  or  to  the  processes  governing  the  universe. Failing  to  properly  enact  a  ritual  can  have  dire consequences: the seas may turn into blood, ancient demons from a forgotten time may escape from their prisons or the sun may lose its flame.

Obviously for my purpose the scope of each need not be so large, nor the consequences — the rewards are smaller, after all — but the structure of it looks like it holds a lot of potential for my purpose.

It pleases me that these are largely system-agnostic, as well. It doesn’t matter if the rules are used in a system that has or does not have feats, having to spend three days a month performing a duty is an inconvenience to the character. It might be handwaved in practice (a particularly character might simply be unavailable during the nights of the full moon), but I think I would like it to come up at least part of the time.

Similarly, it doesn’t necessarily matter what class a character is, and in fact it could be interesting to find a role filled by different characters over time. In The Dresden Files the Winter Knight is a role filled by at least two characters with some significantly different personalities and abilities, with their primary similarity being that they can Get Things Done.

D&D 3e opened the door (in D&D-land) to any race/class combination. To encourage archetypal combinations they introduced the ‘favored class’, where characters of each race could (potentially) enjoy reduced experience point penalties when multiclassing with their favored class — with no effect whatsoever if they didn’t multiclass at all, regardless of class or favored class.

Pathfinder did a better job of it, I think, allowing a small but not overpowering benefit (+1 hit point per level or +1 skill point per level of favored class). Things have changed more from there, with races having more than one favored class, and with (race, class)-specific benefits.

Now, it looks like core races have ‘favored class’ options for _all_ core and advanced classes, and I’ve seen third-party publishers include ‘favored class’ options for all the core races (which I think is a good thing if ‘favored classes’ are a thing).

I’ve asked a question similar to this before, but I think circumstances have changed a bit. ‘Favored class’ options that exist for all combinations seem misnamed.

Perhaps it’s time for racial archetypes on the classes. They’re still optional, so you’re not forced to take them, but half a half-orc bloodreaver (barbarian archetype — and others are possible) instead of picking between +1 hit point per level, +1 skill point per level, or +1 round of rage per level.