Casting a spell successfully requires a successful Casting check. Add your realm stat modifier and your Proficiency bonus.
A casting check is pass/fail: either you succeed or you misfire. A 1 is an automatic failure, but it's not worse than a normal failure. A 20 is an automatic success, but it's not better than a normal success.
If you're casting a cantrip or a spell from an open list or your profession's base list in your own Realm of Magic, the Base DC is 0.
If you're casting a spell from a closed list or another profession's base list in your own Realm of Magic, the Base DC is 5.
If you're casting a cantrip or a spell from an open list in another Realm of Magic, the Base DC is 15.
If you're casting a spell from a closed or base list in another Realm of Magic, the Base DC is 25.
If the spell is a Cantrip or its level is lower than your Character Level, reduce the DC by 5.
If the spell's level is equal to yours, the Base DC stands.
If the spell is five or fewer levels higher than your Character Level, increase the DC by 5 for each level the spell is above yours.
If the spell is more than five levels higher than your Character Level, you can't cast it.
If you're wearing light or medium armor that's restricted while casting, increase the DC by 5. If you're wearing restricted heavy armor, increase it by 10.
If you can't use gestures OR incantations, increase the DC by 5. If you can't use both, increase it by 10.
If you have to cast a normal (non-immediate) spell as a reaction or bonus action, increase its DC by 5.
If you take an extra turn to cast the spell, reduce its DC by 5.
If you expend prepared material components appropriate to the spell list in its casting, reduce its DC by 5.
If you're in a high-magic zone, reduce its DC by 5.
If you're in a low-magic zone, increase its DC by 5.
If your modifiers reduce the DC to 0, you don't have to roll.
If you're outside combat and the DC is 10 or less, you don't have to roll.
If you're proficient in the spell you're casting, add your ability modifier for the realm stat and your Proficiency Bonus.
If you're not proficient in the spell you're casting, add only your ability modifier for the realm stat.
If you meet or beat the casting DC, the spell goes off.
If you miss the target DC, the spell fizzles out.
If you miss the target DC by 5 or more, you suffer a casting mishap. Roll on the appropriate table.
For an attack spell, the casting check and the attack roll are the same.
For a resisted spell, the target makes a Saving Throw to resist. See Resisting Spells.
The Realm Stat Abilities are:
- Channeling - Wisdom
- Essence - Intelligence
- Mentalism - Charisma
- Arcane - Highest of Wis/Int/Cha
Table: Spellcasting DCs
For Example, say 1st-level Magician Mialee is casting Shock Bolt I, the 2nd-level spell from Light Law. It costs her 2 pow. She's proficient in the spell and it's on her profession's base list, so the Base DC for the spell is 0. It's one level higher than she is, so the DC increases by 5. She's taking a normal action to cast the spell and she's not wearing armor, but she's in a Silence field of effect so she can't use Incantations. Her DC increases by 5 more, so she's making a proficient casting check against DC 10. Easy as pie.
In the same turn, Mialee casts the 2nd-level Immediate spell Identify Casting from the Closed Essence spell list Spell Reins as a Reaction to an NPC's casting. It costs 2 pow. Since it's a closed spell list from her realm, her base DC is 5. It's one level higher than she is, so the DC increases by 5. She's still in the Silence field, so it goes up by 5 more. She's making a proficient casting check against DC 15. Little tougher.
Next turn, Mialee tries to copy the spell she just identified, the 4th-level spell Heal III from the Open Channeling spell list Concussion's Way. Since it's Level 4, this one costs 4 pow. It's an open spell list, but it's from another realm than her own. That makes the base DC 15. The spell is 4 levels higher than her own, so the DC increases by 20. She moves out of the Silence field so she can use gestures and incantations normally. She also takes an extra turn to cast the spell, which lowers her DC by 5. Finally, Mialee retrieves crystallized boar's blood from her material component pouch to use as a material component. She didn't expect to be using it with a spell from Concussion's Way, but she prepared it for use with the Physical Enhancement spell list. It seems similar enough that the DM allows it. The final DC for her non proficient casting check is DC 25. Mialee might need to rethink this strategy.