When I first started playing D&D I was utterly baffled about the terminology and descriptions of how to use magic. I avoided it. Some of my players wanted to use magic, so I trusted them to learn their own class.
This was a mistake 😆 Whilst they grasped the basics of their class, one player in particular took liberties with functions that would have restricted him. This was partly because neither of us fully understood why the mechanic was there in the first place, or how it was actually supposed to be quantified. It took both of us well over a year (and a few squabbles) to get to grips with magic casting in D&D.
To try and save you pain, I have done my best to recall our early confusions and answer them in one place. If you have a question that isn’t answered here, please let me know! The grammar and terminology of The Players Handbook is not always as good as it should be, and the vagueness and confusion it leaves as a result is frustrating.
What is a spell save DC?
You’re probably aware that DC means ‘difficulty check’. But what is a spell save DC? How do you work that out? Is it the GM who decides?
If a creature or object has to succeed a spell save DC, this is a predetermined score. The score is determined by the person casting the spell. Every spellcaster has a ‘spell save DC’, which they should work out before attending your session. You work it out as follows: 8 + proficiency bonus + spellcasting modifier. Let’s say our wizard has a spell save DC score of 15. This is how difficult it is to overcome any spell specifically cast by the wizard.
The next time your wizard casts a paralysing spell and the creature has to make a Wisdom saving throw to resist the effects, the creature must roll either a 15 or above to successfully avoid being paralysed. Example play:
Wizard: I cast paralysis on the goblin! They must succeed on a Wisdom saving throw.
GM: What’s your spell save DC?
GM: *rolls dice + goblin WIS* They scored a 16! The goblin quivers and grimaces, eyes bulging, as it shakes off the effects of your paralysis spell.
What is my spell attack modifier?
Just like a fighter who must roll to attack with their sword, you must accurately hit a creature with Eldritch Blast. If a spell says something like, ‘make a ranged spell attack against the target’, you will roll the following:
d20 + spellcasting modifier + proficiency bonus.
If the total beats the creature’s Armour Class, then you hit!
Spellcasting ability depends on class.
For Wizards, Fighters (e.g. Eldritch Knight), and Rogues (e.g. Arcane Trickster) your spellcasting ability modifier is Intelligence.
For Clerics, Druids, Rangers, and Monks (e.g. Four Elements) your modifier is Wisdom.
For Bards, Paladins, Sorcerers, and Warlocks your modifier is Charisma.
Eldritch Knight: I cast Eldritch Blast!
GM: Is that a spell attack? Please roll to hit.
Eldritch Knight: A d20 + my Intelligence + proficiency… 18!
GM: Their armour class is 12, excellent. Please roll damage.
Eldritch Knight: Full damage! 10!
GM: You blast that bitch to pieces.
What is a focus and why do I need one?
The purpose of a focus is so that spellcasters do not need to always use material components when casting a spell. If they are holding their focus, they don’t need petals or an iron rod. HOWEVER. If a cost is indicated for a component (e.g. a ruby worth 1000 gold pieces), a character must have that specific component before he or she can cast the spell. This is the same for material component’s that are consumed by the spell, the spellcaster must have the component each time they cast it.
Does that sound annoying? The purpose of a focus is to make meaningful choices during combat. A spellcaster needs one hand free to hold their focus or component. If the sorcerer has to put away their staff in order to help carry someone, they can no longer cast spells that require components. They have made a meaningful choice. The same with applying costly materials – it’s usually because the spell is powerful. To stop you from casting spells whenever you want that would cheapen any challenges, you need to work to have the materials or wealth on hand.