Kingsoul

All credits go to Rose Knight's homebrew on YouTube

Once per long rest you can attempt to cast a spell without expending any material cost or spell slots. In order to negate the cost of a spell you must roll an ability check DC of 16+ the spells level VS your spell casting modifier. You cannot add any bonuses to this roll unless granted by the DM. Failing this check will expend the spell slot without casting the spell.