How would you barna10 handle the spells themselves? Import spells from another retro-clone? Swords & Wizardry or Labyrinth Lord would work pretty well. Though I think you'd have to really custom craft a lot of them.
It is an interesting take on what many feel is a problem with spell slots, and no spell point system has really caught on widely. This might be a way to solve that.
In general, I quite like this idea and do think there is room for a Dr. Strange, Zatanna, Raven (one of my favorites), Magik, Etrigan, Brother Voodoo, Dr. Fate, and The Spectre.
Maybe this could work for Scarlet Witch and her son Wiccan too?
I have a Guardians Companion book in the works, I could see including something like this. I already have several new options and a ton of NPC super heroes/villains and adventure hooks written up. Just need to find the time after I complete the Princess of Mars adventure to work on it.
I left it open in my description as you bringing in spells "from your favorite OSR version". I'd use spells from BECM myself, my preferred version. I don't think it'd matter much which exact versions you use as it will take several levels before the raw powers of the spells challenge the Guardians! super powers.
Regarding crafting the spells, I'd use them as-is and just let them feel archaic. I'd let the players develop updated spells unless they maybe found them after defeating magical villains or something.
Glad you liked it Also, keep me in mind if you want some play testers. The kids and I can give 'er a spin.
I should caution that I don't work very fast and have a terrible habit of mentioning projects I'm working on way too early. I still have a batch from 2018 I mentioned on my blog that are all in various stages of completion from 50% to 90% done.
After mulling this around and playing a bit with the kids, I came up with a different approach for the "spellcasting class".
Instead of an entire class, I created a power called Spellcasting.
The normal level allows the character to cast 1st - 3rd level spells. Superior allows 1st - 6th level, Ultimate 1st - 9th.
Spell selection can be limited and require taking the power several times to get M-U spells, Cleric spells, Druid spells, etc. I'd use this option in a campaign that interacts with a fantasy world or one that is deeply steeped in the supernatural.
Or, as in most "supers" campaigns, that distinction by category of magic is unnecessary. You can simply allow the character to learn and cast ANY 1-3, 1-6, or 1-9 spell regardless of which spellcasting class would normally be allowed to cast it.
Casting spells takes 1 power point per spell level.
Each time the power is gained (normal, superior, ultimate), the character gains three spells of either choice, random rolled, or GM determined. The levels of the new spells are 1-3 for normal, 4-6 for superior, 7-9 for ultimate.
New spells can be gained by any means that make sense for the game (ie learned from reading an ancient tome, through psychic learning, from a skill chip, by eating the brain of a spellcaster, by watching Harry Potter movies, whatever...it's supers, who knows )
Much simpler than a new class. Also, this approach allows for "natural" casters so an Exotic or Supernatural character can be born with spellcasting abilities, for instance, or a Power Wielder could be a Superhuman by virtue of spending a decade in a monastery on top of a frozen mountain where he learned the mystic arts.
I like the simple approach and it seems to go more in-line with the flavor and themes of Guardians!