D&D 5E Simple magic crit fails

[Khelon Testudo]

In this thread @rustydm asks for spell failure mechanics. He appears to be looking for published material - perhaps as form of quality control.

But it did inspire me to create this simple rule system:

A critical spell failure happens on the roll of a 1 by the caster, or a 20 by the saving throw target on the first attack roll or save (since spells may have multiple of either).

The blowback is 1d4 damage of the damage type of the spell.
If the spell doesn't have a damage type, the spellcaster suffers the effect of one roll on the table for the Confusion spell until the end of their next turn.

Aside from the whole issue of critical fails being more dangerous to PCs than NPC's, are there any major issues this might cause? (I might rule it doesn't affect innate spells, or Legendary foes get to use a legendary action to negate it. And it wouldn't suit a horror or very serious game.)

 

[Eltab]

The Wild Sorcerer 'random event' table has some entries you could use. Turning neon glowing green is good for L1 character drawbacks, but summoning a Modron would be more suitable for higher-level accidents.

 

[Khelon Testudo]

That's an idea. Should the critical failures scale with the level of the spell cast?

 

[Li Shenron]

Aside from the whole issue of critical fails being more dangerous to PCs than NPC's, are there any major issues this might cause?

I think this is a fairly simple rule and the drawback isn't that big, so I don't think you would have issues.

Except maybe the fact that this rules affects combat cantrips a lot more than levelled spells. If you have a spellcaster regularly using a combat cantrip instead of a weapon, they'll be doing a magic attack roll fairly often. Though probably still not as often as martial types making weapon attacks, they'll still be suffering the drawback damage frequently. But then maybe it's still once every adventuring day or two.

I don't even think that with such small damage there would be a balance problem here, but rather a possibility that the drawback becomes only annoying to the players if it happens too often, which is one of the common reason why groups using attack fumbles sometimes regret it.

 

[Khelon Testudo]

That does also suggest the blowback scaling with spell level. Perhaps cantrips only do one point of damage on blowback, while leveled spells do 1d4?
Or 1d4 for levels 1-2, 1d6 for levels 3-4, 1d8 for levels 5-6, 1d10 levels 7-8, 1d12 for level 9 spells? Non-damage spells wouldn't change.
I don't want to go too deep into the weeds here. Wild magic sorcerers are unpopular for a reason.

 

[jgsugden]

Why have the 5% (or nearly 10% when advantage/disadvantage is involved) chance of a magical mishap? Would it be anticlimactic to have the BBEG undone by his own spellcasting? Or the heroes to die because of a random bad roll at the wrong time on a spell that they have been casting forever?

If you're going to do it, I suggest doing it for a purpose - to make magic the control of magic a real concern and something the PCs need to struggle to control. If they wait to develop the skills, they can manage the magics safely. If they want to, however, they can try things too advanced for them at the risk of causing catastrophe.

If I were going to have these rules, I'd have it apply only to arcane casters (Wizards, Sorcerers, Bards, Warlocks, Arcane Tricksters, Eldritch Knights, etc...) I'd allow them to preselect spells that are normally above their level (the mechanics of this preselection differing by class), but give the spells a chance of failure and disaster if they attempt them before they've mastered them.

 

[Umbran]

Aside from the whole issue of critical fails being more dangerous to PCs than NPC's, are there any major issues this might cause?

Annoyance, which is non-trivial..

At first level - possible death, as they may only have 6 hit points to begin with.

 

[Eltab]

That's an idea. Should the critical failures scale with the level of the spell cast?

Yes, just like a toddler falling off his tricycle gets smaller boo-boos than a child falling off a bike gets ouchies ... or what injuries an adult racing a motorcycle can cause.

I don't have a good grasp of scale, but messing up a cantrip should cause a cosmetic, non-mechanical result. You turn colors, the enemy's hair becomes a bouquet of flowers, something funny / embarrassing and play resumes after a laugh.
Messing up a Fireball is liable to hurt the caster and maybe those around him, enough to notice but not kill people outright (NPCs on the other hand...) "Minimum damage" should be a legit possibility.

The effects might be rolled randomly with Spell Level adding to the table result (bigger is worse) or you as DM could set up a few notes beforehand. In this case, be thematic: Summon XYZ might bring in a Dire XYZ or a very hungry one or a youngling; rolling a 20 to save vs Charm Person means he sees right through you (and if a caster he can make it boomerang); your Lightning Bolt leaps upward into the nearest tree or it barely gives anybody a tingle.

How does your group respond to failure or comedy / irony or disrupted plans? If the answer is "badly", then you might use Counterspell or Create Dead Magic Zone rules to indicate the failure.

It might be fun to postulate a world where magic is ill-understood and barely controlled, so it sprays off unexpected side-effects. I don't know that I would want to campaign in it (I plan like a Tactician) but I could visit the place.

 

[Khelon Testudo]

Summons don't have rolls. Which I agree, is a missed opportunity where critical fails are involved - and very in theme for a critical fail.