Ahoy there GreatestHonor amigo!
I was wondering what level a spell would need to be to cause an extinction level event (limited to just a planet).
To simply destroy all life on a planet you could possibly do it in a bunch of different ways, trying to recall a few spells off top of my head...
Volcano is a Level 16 spell
Land of the Dead is a Level 17 spell, that Animates all the dead in an entire country.
Sink Continent is Level 18
Extinction Asteroid (aptly named) is Level 19
Moonfall is Level 20
Superlaser is Level 21
Note that Gods will get +1 Higher Spell Level Slot per Divine Rank (and some Boons can extend these). So Odin* (Divine Rank 6) can cast a 10th, 11th, 12th, 13th, 14th and 15th level spell.
*His Alt Wanderer (Mythic Form) at least
Plus with the Overcasting System you can attempt to cast spells several levels above your maximum...at a risk.
Also does it differ depending on the events? For example would a super-plague differ from a mega storm or a mile-wide meteor?
Without going into details, above a certain point the most powerful spell 'factor' (typically the scale) determines the spell level. Therefore if I want to affect a town (lets say) it will be a Level 14 spell. So if I want to blow-up the whole town, animate the whole town, cause the whole town to levitate, planeshift the whole town to Hell its always a Level 14 spell because the scale factor is greater than the effect factor (fireball L3, Animate Dead L2, Levitate L2, Plane Shift L7 etc.)
UNLESS the effect factor (like killing an immortal with no save, Time travel, etc.) is higher than the towns scale factor, the Spell Level is consistent.
And unrelated, where would you place the Endless from the Sandman comic? Death is obvious, but wondering if you would have Destiny be a bit higher/the rest of the family lower.
Death is Challenge Rating 100 in these new Rules, which is Divine Rank 22. Art is already done for Death so he/she/it will show up at some point - likely not this book though.
While I am familiar with Sandman I have never read it nor watched the show - my girlfriend mentioned a few nights ago scrolling through Netflix "Hey you would like this show" - the show being Sandman. I've just never been a huge Gaiman fan - but I might give it a go.
As to the power of the other Endless, maybe Destiny is more powerful, the others less so. Your guess would be better than mine.
God Rules Progress Update: I was unhappy with a lot of the Divine Boons, functional but not exciting enough. So I am in the process of combining about 250 (of the 400+) into each other to have 125 'better' Divine Boons. More interesting flavour text. Something Passive + something Triggered. More interesting Lore.
So 25-30 per tier rather than 41...albeit the sections are now longer.
So far its all going great although, as ever, that's set me back a week or two, hopefully still get the Chapter finished by the end of July. But this chapter will now be awesome to read because virtually every Boon has a few sentences or short paragraph of Lore which are some combination of A. Adventure Hooks. B. Lore Snippet. C. New Bestiary Foreshadowing...and obviously the higher the boon's 'Tier' the crazier those get.