The party might find itself forced onto a non-native setting. They are originally from the Mystara setting who have Immortals instead of deities. I would like to play true to the new setting, whichever it may be, so I was wondering on your thoughts regarding divine spellcasters (cleric, paladins...etc): How do they access their divine powers/spells if they are on a different material plane?
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So how does a cleric now cast spells and use his/her divine powers? Does anyone know of a creative idea as well as a mechanical system whereby through an additional cost to the cleric he/she is able to access their powers/spells?
The group strives for a sense of realism/grittiness so true balance however is not an issue with us, but I would also prefer not to seriously gimp the cleric for an unknown period of time.
EDIT: Apologies, I was not clear above given my wording, this is not about following canon, but a flavourful way to, subtly through the mechanics, reflect the implied 'distance' between cleric and the immortal/deity he worships and the hardship in refreshing his divine abilities when he travels to different settings on the material plane.
TheCosmicKid came up with some great suggestions I intend to use.
In 2e you had to cast a (2nd-level if I recall) spell each day to contact your deity in order to be able to prepare spells at all. 2e also had a whole lot of other restrictions when moving around the planes or the crystal spheres. This was in harmony with AD&D's general restrictive and punitive way of limiting things.
None of those restrictions are a part of 5e philosophy.
I'd say that if you are in a crystal sphere where your deity isn't known, you might not be able to use the 10th-level requesting a miracle power, and/or you might have a chance of failure when casting a
commune spell. Beyond that...it's all in the role-playing. Maybe the DM decides that your deity doesn't hear your prayers, or that they take the long scenic voicemail route and get heard a month late. But spellcasting ought to work perfectly no matter where you are--it's a core feature of your class.
I would suggest strongly thinking through any limitations you create and weighing them against how 5e philosophy deals with other things converted from prior editions. If you do decide to go punitive, realize that you are making an exception to how 5e normally works, and
make sure it is worth it to your game. As a player, it would have to be a pretty good reason for me to not get a sour taste in my mouth about that (and I'd definitely want to know ahead of time during character creation).
Clearly their divine abilities are granted by the Immortals who are not the 'deities' in this other setting (Greyhawk, Forgotten Realms, Dark Sun...etc) they will find themselves in.
An utterly meaningless distinction that 5e should toss.
Immortals: Phenomenal cosmic power
Deities: Phenomenal cosmic power
Immortals: Portfolios, areas of control/interest
Deities: Portfolios, areas of control/interest
Immortals: Hear prayers and give spellcasting to followers
Deities: Hear prayers and give spellcasting to followers
Immortals: Have inconsistent travel restrictions about visiting the mortal world
Deities: Have inconsistent travel restrictions about visiting the mortal world
Immortals: All (theoretically, but not proven) used to be mortals
Deities: At least some used to be mortals
Immortals: Include among their Thor, Osiris, etc
Deities: Include among their number Thor, Osiris, etc
It's a completely arbitrary semantic distinction that only exists because BECMI did things a bit differently than AD&D. It should have been reconciled in 2e when they converted Mystara to AD&D, but it wasn't. I recommend you utterly scrap it and consider them to be the same thing.