Homebrew Need help with homebrewed Magic Surge mechanics

[Ranger Aarakocra]

Hey all, I'm working on a homebrewed D&D setting, and the main premise is that magic has been rendered unstable and sometimes does not even work. A formula for rolling after every spell casted is proving difficult to make. Here are the aspects that need to be a part of it:

• Level of the spell casted
• Magic instability rating of the area (1–8)
• Proximity to a leyline (channel of raw magic) in feet increments

Magic instability ratings for reference:

1: Magic just... doesn't work.
2: Magic is highly likely to fail.
3: While magic is more likely to fail than normal, you can still safely spellcast... for the most part.
4: Just the average amount of magical influence.
5: Spells are slightly more likely to surge here.
6: In an average combat encounter, you will definitely surge multiple times.
7: Spellcasting here is very likely to lead to a surge.
8: Cast Goodberry and grow a third eye, >70% chance of a level one spell surging.

Speaking of which, here's some other percentages for the likelihood of a spell surge:
In an area rated 4, there is a 5% chance of a level one spell surging. 5 = ~10%. 6 = ~24%. 7 = ~44% 8 = ~76% (these are probably unbalanced; this is just a rough estimate.)

Do you have any ideas for what kind of dice to use (d20, d100) and what the formula would look like? I'd appreciate any feedback.

 

[Ulorian - Agent of Chaos]

Do you anticipate any player rolling up a spellcaster for this campaign given these constraints? I know I wouldn't want to! Or is the idea that the party is pure martials? Or do you feel that spellcasting is too powerful and this is a mechanism to address that?

 

[aco175]

@Ranger Aarakocra welcome to he site, sounds like a cool idea but a heavy lift.

I like the spell-fail chance by level of spell. One issue is that you are adding another roll(s) every time someone uses an action. This tends to slow things down. If the payoff is worth it, then go for it. Not sure what the end point is though.

There should also be items, unless magic items also have problems, that allow you to drop the spell-fail percentage. The Wand of Potter takes 20% off so not you can always cast cantrips and level one spells unless you happen to be near the center of the meteor crash, then you are back to normal chance.

There also seems that the ley-lines would have grown towns and mage towers to help them cast without failure. Makes sense if this is the best area. Depending on how long ago magic became a problem, there might be all the dungeons along these lines as well.

This brings things to why the magic is having a problem. Is it just always been so and it is what it is. Did a meteor crash long ago and affects things the closer you are to pieces of it. Did a god curse things. Is there something the PCs can do?

 

[GMMichael]

I'd appreciate any feedback.

Welcome to the trenches!

D&D's Tome of Magic (circa 1990) did something similar with Wild Magic. Each casting would roll on a table for power level variation, and there was a d100 table for wild surges (special spell results). It's worth a look if you have good Google-fu or a proper library system.

 

[Ranger Aarakocra]

Do you anticipate any player rolling up a spellcaster for this campaign given these constraints? I know I wouldn't want to! Or is the idea that the party is pure martials? Or do you feel that spellcasting is too powerful and this is a mechanism to address that?

Upon further reflection, this nerfs casters way too much. The purpose is to add flavor to the world, not fix the martial-caster divide.

 

[Ranger Aarakocra]

@Ranger Aarakocra welcome to he site, sounds like a cool idea but a heavy lift.

I like the spell-fail chance by level of spell. One issue is that you are adding another roll(s) every time someone uses an action. This tends to slow things down. If the payoff is worth it, then go for it. Not sure what the end point is though.

There should also be items, unless magic items also have problems, that allow you to drop the spell-fail percentage. The Wand of Potter takes 20% off so not you can always cast cantrips and level one spells unless you happen to be near the center of the meteor crash, then you are back to normal chance.

There also seems that the ley-lines would have grown towns and mage towers to help them cast without failure. Makes sense if this is the best area. Depending on how long ago magic became a problem, there might be all the dungeons along these lines as well.

This brings things to why the magic is having a problem. Is it just always been so and it is what it is. Did a meteor crash long ago and affects things the closer you are to pieces of it. Did a god curse things. Is there something the PCs can do?

I’m definitely working on the impact of magic on civilization, how it can be fixed, etc. Currently, I have a prototype for these magic mechanics. Made it on the Homebrewery. Attached below. Thoughts?

 

[aco175]

I seem to be lost on these charts you have. The first thing you mention is the level of the spell, but the chart shows something called magic impact with modifiers starting in the middle and not not at the bottom. Same with the other chart about zones. I can get that some places have a better chance of casting a spell and some a worst places, but think that the better places would be level 1 places and the then go to level 9 as the worse.

The charts should be easy to use as players using casters need something simple to add to the complexity of using a caster in the first place.