[quote=@SilverPaw]
any policy on new spell creation? From the manga so far it often seems to be...desperation or need based on the short term, a result of studying/training/inspiration on the long term.
[/quote]

The series proper shows that most new spells are learned/created through training, and apparently there's some implication that some forms of magic/spells can be found within  the setting's Dungeons? Being that some forms of magic are more common than others, I would also assume that people with compatible magic types could somewhat "teach" their spells, or at least variations, to others.

As far as the "new spell shows up in dire moments" type stuff, Black Clover actually does a good job of tying that into character development, and not just the usual shonen last-moment turnaround tropes. The desperation and need, or the near-death experience, often serves as the tipping point to really make whatever realization stick in the character's mind, but it's their own personal growth and epiphany that triggers the spell and whatever form the spell takes will reflect that. For example, when the character Gauche (Mirror Magic) learns to rely on others instead of just himself, he learns to make mirror-image clones of himself and his allies.

In the RP, whenever a character "qualifies" to gain some new powerup or some sort, I'll notify them in some fashion. It might be a little gamified, like reaching a level up after a certain number of milestones, but I definitely want to emphasize character growth along with the classic power creep.