Ah, it's been a while since I argued we don't need X or Y class. I've defended the Cleric before and while I stand by what I said about Clerics being a distinct and important class unto their own, today I look at it from a different angle. While I personally like the Cleric in DCC, I'm also a big supporter of having as many different ways to run the game as there are people to play the game. Don't think of this as me pooh-poohing the Cleric, but rather exploring different ways to run them.
In the post linked above, I mention having seen other Judges' discussion of Clerics being replaced by Wizards, but never have I seen a proper how-to. So here's how to do it. Each heading below provides both the Cleric concept being converted and the Wizard concept it maps to. The resulting Cleric is one that is more of a pure caster than the hybrid fighter-caster we usually see - more suitable for a priest than a paladin.
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Conventions for Clerics as Wizards
The Cleric class is no longer a distinct class of its own. Instead, the Wizard has broader access to spells and patrons which allow for the flavouring of a Wizard as a servant of a divine power. Many of the features given to Clerics have a lot of functional crossover with those of Wizards even if they do not use the exact same mechanics, so much of the conversion here is fairly direct.
Deities / Patrons
Bobugbubilz and Azi Dahaka are already offered as both Cleric deities and Wizard patrons, both of whom seem more like a powerful entity within the universe than a deific entity from beyond. Incidentally, they are also both demonic (hardly relevant, just interesting). A world with Clerics of slightly more grounded powers than literal Gods might make more sense with patron relationships such as these instead of strictly faithful worship.
The rule here is simple: A Cleric is a Wizard who has taken a godly figure as a patron. All godly figures are now potential patrons. If a player plays their Wizard character as a worshiper of a deity in the world, the Judge should allow an opportunity to gain patronage and treat their power as if it comes from that deity (or through faith itself).
Canticles / Patron Spells
The DCC Annual already gets bloody close to patron spells with the inclusion of canticles for deities. If your Cleric-Wizard chooses a deity from this list, most of the work is already done (although higher level spell checks may need to be written, as many canticles are basic single-level effects). Beyond that, it's no harder for the Judge to create these than it is to create regular patron spells.
A godly patron's patron spells should follow the usual format for patron spells and effectively replace any canticles.
Divine Aid / Invoke Patron
Divine Aid is effectively replaced by Invoke Patron. This doesn't really do the same thing, but it is the result of you calling upon your patron for help in a time of need. An Invoke Patron spell can be written that works thematically for divine aid from a particular god. Spellburn can replace the disapproval as a downside.
Disapproval / Patron Taint
Disapproval tables will need to be shrunk down to create a patron taint table and the more permanent options are the ones that should be retained to achieve the patron taint style. Don't keep the one where you have to pray for 10 minutes, do keep the one where Pelagia gives the character bulbous fishy eyes.
Lay on Hands and Turn Unholy / Spells
Treat these two abilities as spells on the spell list. They essentially already have a spell effect table with simpler formatting. And on the note of accessible spells...
Cleric Spells / Wizard Spells
There is no longer any delineation between Cleric and Wizard spells. Any and all spells of the appropriate levels can be selected from in the usual ways (randomly on advancement, discovered through adventuring, granted by a patron, research).
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And that's it. You know, I didn't expect it to be quite that simple. It's fairly easy to make the argument against Clerics after having written down how each of their mechanics map to each other, one-to-one. Clerics start to feel like alt-Wizards, and it's entirely possible using the conventions above to run them as exactly that.