Arcanist's Conservation of Magic

You channel an entropic essence that allows you to harvest the residual energy from your failed spells to fuel your magic. As long as you remain concentrated on this spell, any time you cast a spell that does not successfully produce the desired effect, you have the chance to regain any spell slot used in the process of its casting. If the spell involved a spell attack roll that missed or a saving throw that did not produce an effect on a successful save, you regain a spell slot equal to the expended level. If the spell caused a reduced effect or half damage on a successful saving throw, you regain a spell slot equal to half that of the expended spell level rounded down. If at least one creature failed a saving throw against the spell, then the spell is considered successful and a slot is not regained. You can elect to regain a spell slot of a lower level than the maximum of what this spell effect specifies, but you cannot regain a spell slot of higher level than that which was cast. You cannot regain additional spell slots beyond that which you are capable of possessing at your current level. If you cast a cantrip that does not succeed on its desired effect, you can grant yourself advantage on the attack roll or impose disadvantage on your target’s saving throw the next time you cast that specific cantrip while you are concentrating on this spell. If this spell lasts for the duration of its casting, roll a percentile die. If the number rolled is lower than half of your character level rounded down, then you regain the spell slot used to cast this spell and you cannot cast this spell again for 24 hours.