New spellcasting mechanic: the Mana Check

By default, D&D uses Vancian magic, and has done since its earliest days, more or less. Vancian magic is where spells are prepared in advance and can only be used a finite number of times. It is sometimes known as ‘fire and forget’ magic, or, more disparagingly, as ‘utility belt’ magic. The term ‘Vancian’ comes from fantasy writer Jack Vance, and this is how spellcasting works in Vance’s novels. (Fun fact: the name ‘Vecna’ is an anagram of Vance.)

Vancian magic has its place. It helps to create game balance. It has been part of the game’s fabric for a long time. But it can also feel a little artificial and unintuitive. It locks you into thinking about magic in a particular way.

In this article, I present a variant system where spellcasting is more unpredictable but also, potentially, more organic. You don’t have to use it. It isn’t thoroughly playtested. But it sits as an alternative to the usual D&D method of tracking spell slots and spells per day.

How it works

With this variant system, a character who has the Spellcasting feature makes a mana check instead of using spell slots to fuel spells.

Instead of gaining a number of spell slots each day to cast your spells, you must make a DC 10 mana check after you cast a spell. By default, a mana check is 1d20 plus your proficiency bonus (but does not include your spellcasting ability modifier). For easy spells, you roll with advantage. For hard spells, you roll with disadvantage. The difficulty of a spell is determined by the table below: Spell Difficulty per Level. If you succeed on your mana check, nothing happens, and you can keep casting spells. If you fail, you can no longer cast spells of that difficulty.

By default, this is a system for ‘full’ casters: bards, clerics, druids, sorcerers, and wizards. I have tried an alternative system with ‘half casters’ like paladins and rangers, but I think it needs a bit more work.

As an optional ‘burnout’ rule, you might allow spellcasters to take on a level of exhaustion to keep casting spells. A spellcaster can also cast spells at a higher level, as normal, but doing so may make the mana check more difficult.  

Spells of 6th level and higher are particularly taxing to cast. A spellcaster can only cast one spell per day at each level, and no mana check is required. Cantrips, on the other hand, can be cast at will, as usual.

This system can be applied to monsters that cast spells using spell slots, but you will need to work out the spellcaster’s proficiency bonus based on their spellcasting level. A flameskull, for example, casts spells as 5th-level spellcaster, so its mana roll would be +3 (the same as a 5th-level wizard). To be honest, I’m not sure it’s worth the effort, since most NPC spellcasters are dead within three rounds anyway, but the option is there if you want it.


Let’s take a Mialee, 7th-level wizard as an example. 1st-level and 2nd-level spells are ‘easy’ for her: she can roll her mana check with advantage. 4th-level spells are ‘hard’: she rolls with disadvantage. For 3rd-level spells, she makes a mana check without advantage or disadvantage.

In the first round of combat, Mialee casts magic missile, a 1st-level spell. Mialee’s player rolls damage as normal and then makes her DC 10 mana check. This is 1d20 plus her proficiency bonus, which is +3, but she rolls with advantage as 1st-level spells are ‘easy’ for her. She rolls 20: easily enough to keep casting spells.

On her next turn, she casts fireball, a 3rd-level spell. Her enemies make saving throws as normal, and she rolls damage. She then makes another mana check, this time without advantage (fireball is neither ‘easy’ nor ‘hard’). She rolls a 3: even with her +3 proficiency bonus, that’s not enough to succeed. If Mialee wants to cast fireball again, she would need to cast it at a higher level, which would be a ‘hard’ mana check.

In desperation, Mialee decides to do this on her third turn. She casts fireball at 4th level. After rolling damage, she makes her mana check, this time with disadvantage. She gets a 10! It looks like she can keep casting fireballs – for now.

In play

As stated at the outset, I haven’t playtested these mechanics extensively. However, when we tried these rules as part of my regular Monday-night game, they seemed to work well. And the maths checks out, too (I think). On average, you you should be able to cast the same number of spells per day as a normal spellcaster of your level, give or take.

The biggest difference you might see with this mechanic is that spellcasting becomes a bit more of a gamble. Spellcasting is less reliable than before: you might find yourself out of spells in the middle of a boss fight, for example. But it swings both ways. You might find yourself suddenly powered up by being able to cast far more spells than you normally would.

Try it out. Let me know in the comments below how you get on.

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