I am playing Pathfinder and I have a Rogue 7 Magus 3 build. I have a Magus Arcana called Spell Scars which says I can add a total of 18 level spells (adding spells is similar to a Scribe Scroll feat). Can I add 0 level spells for free?
Spell Scars uses the same item pricing guidelines as scrolls, which, as per Pathfinder's Item Creation rules:
Spell Level: A 0-level spell is half the value of a 1st-level spell for determining price.
The Spell scar Arcana doesn't explain how it deals with space for 0th level spells, so I'm going to extrapolate that it is similar to how much space a 0th level spell takes up in a spellbook .
Space in the Spellbook: A spell takes up one page of the spellbook per spell level. Even a 0-level spell (cantrip) takes one page. A spellbook has 100 pages.
Given that a 0th level spell takes up one page of a spellbook, one can probably assume that a 0th level spell scar takes up the equivalent amount of space on your skin as a first level spell scar.
This is how I would rule as GM at least.