[@Klomster] Thanks for the bump. Realistically, what you're asking depends on the magic reserves available to a deity. Having consulted with gammaflux on this, we've established that typical PC deities, at roughly 1.25x the strength of the weakest deities, could exert most or all of their Arcane and Divine power to reduce to energy the mass of a decently-sized mountain range, though deities focused on less offensive disciplines such as healing may have issues with channelling all that as pure destructive force. Standard PC mortals (SPCM), at 0.75x the strength of the weakest deities and therefore possessing around 60% of a standard PC deity's power, can reduce to energy around 60% of the mass that a standard PC deity (SPCD) can.

However, it should be noted at this stage that the power is rather relative between the two groups. Whilst a SPCM would be soundly thrashed in a one-on-one fight against a SPCD, and the deity's mere presence would be considered a huge deal to most mortals whilst the same is not true in reverse, the fact that a SPCM is as strong as they are would be considered a major feat by most of their fellows, and they would likely hold major positions within at least their race, if not the religion as a whole (and I recommend that SPCMs are built around roughly this specification unless there is a good reason to avoid doing so); by comparison, a SPCD is rather small fry amongst the ranks of the divine, and Alithos would likely be able to take on every PC-level deity alone with little more than scratches from them. Not to mention that a good portion of a deity's power, size dependent on the deity themselves, is Divine rather than Arcane, which is a further damper in many cases if they don't want to expend the former.

Since we're on the topic, Divine magic is accumulated rather more slowly than Arcane magic recuperates. Any being acquires more Arcane mana at a rate proportional to their Arcane mana reserves, such that even if they fully expend all of their Arcane magic, it will recover entirely with about a full day's rest, give or take up to an hour. By contrast, Divine magic has no explicit limit on how much can be accumulated, but methods of acquisition are by their nature far slower:

-Active worship of a deity by any mortal will grant them some Divine mana, adding up to a reasonable amount over the worshipper's lifetime, with a minimal gain over time via being a passive part of that deity's worshipper base;

-Temples, churches, statues, and other monuments dedicated to a specific deity will grant that deity Divine mana based on the amount of dedication put into them (based on traits such as size, effort of building, build quality, how well they exemplify the deity's merits, and so on), with relatively minor monuments providing less mana per time unit than even a single active worshipper, whereas large and substantial projects such as a very large cathedral would even grant mana during its construction as though it were a form of mass worship and continue to provide a significant stream of mana even after construction ends, though in any case, the monuments will provide Divine mana until they become decrepit enough to not be significant to the faith of the deity any more, a potentially much greater timescale than any mortal could provide for them;

-Sacrifices to a deity, of any sort, will provide an immediate and comparatively large boost of Divine mana, though this is obviously only a one-time thing per sacrificed being, and varies in significance depending on the sacrifice itself - food and drink sacrificed "in spirit" will only provide small boosts, whilst animals may provide a somewhat greater boost depending on how well they're prepared, and mortals will provide more mana based on the preparations taken, and the devoutness of both sacrificer and sacrificee, with the greatest boosts coming from fanatically-loyal worshippers placed into either role (perhaps both simultaneously, if they commit ritual suicide in their deity's name), though a worshipper of another deity sacrificed by a sufficiently-loyal worshipper can provide almost as much strength.

Deities can also provide other deities with their own Divine power, though this is a relatively uncommon occurrence given that it's a rather precious resource; aside from transfusions via direct contact, the most common way for this to be done is by soaking food or drink with Divine energy for another deity to consume, though this only has any significant effect within about two weeks of the initial energy soaking, since it rapidly drains away over time. Notably, a mass sacrifice is the only way to bring a new deity into existence quickly, as energy obviously cannot be transfused to a being which doesn't yet exist, and the initial requirement to bring a new deity into being is so large that any other method of worship will almost certainly take anywhere from a hundred to a thousand years to achieve, whereas the comparatively large boost from a sacrifice of a large number of people, performed all at once, could well bring a new deity into existence almost immediately, though if the entire worshipper base died as a result, it could be that the deity is immediately put into a situation where they have to start preaching their own word to gather replacement worshippers.

Speaking of sacrifice to bring a new deity into being, expect my character for the game to be created shortly.