Dangers of the Arcane

GM NOTE: This entire change in how magick and the system works is entirely optional and should be discussed with players before playing this way. It does slow down combat a slight amount as casters now have to roll an extra dice, and if things go poorly, there can be big consequences that eat a bit more time. So that is something to consider. If one wishes to merely run this as a 5e supplement, using spell slots without having to adapt to an entirely different set of rules in regards to magick, that's fine. However you think you can capture the feel. Perhaps you would rather it just be they must make a saving throw of their casting ability against a simple base DC, that's acceptable. Perhaps you will wish to just leave the consequence system almost entirely, basically just rolling a d20, and unless a 1 is rolled, nothing happens? Totally fair. You can just entirely ignore it as a thing, but be aware it will make Valerick's lore and gameplay feel a bit....odd and strange in setting as if there are no negative consequences, why is their such a harsh system in place in regards to arcane magick?. But ultimately it is up to you as a GM and your players at the table to discuss all this openly and decide the approach you prefer. What is presented below are the baseline concept and consequence system in place.

Those whom manipulate the arcane on Valerick are handling a great and terrible power, capable of amazing, and horrifying things. The raw power that Manna contains, the raw power that bleeds in from the Void, can simply not be overstated. However this eldritch power is not merely their, docile and waiting to be used. No if you were to ask any magister, regardless of their Order, of the sort of manna they manipulate, they would tell you what they do is not a willing or aided action. They walk a knife's edge with their abilities, for such an ancient and powerful force as Manna, as the arcane elemental currents that forged the very reality of the world and the cosmos itself? Such a thing has a....presence all its own, and no amount of it is willing to just...be used by some mere speck, a creature that is a mere speck on the timeline by comparison of the universe. No these energies are quite opposed to being manipulated and bent to the will of mere mortals, and resists such efforts in every way it can. That is to say nothing of the mental awareness and discipline one must have in spell-weaving to do everything correct, and to insure you do not draw in any Void taint, you manage to seperate what you need from the corruption in the Aether that is ever present now.

Corruption and Miscasting

Corruption: There are eight corrupting influences from the Void, each tied to one of the Ruined Gods. Wrath, Pride, Sloth, Lust, Greed, Gluttony, Envy, and Cowardice. These are what accumulate in corruption upon one's very essence and can negatively impact spellweaving. If you have any of these at 2 or more, you now suffer a Major Miscast if you roll a natural 1, and your spell doesn't work if you roll a failure. If any of these are at 5 or higher, you are at Disadvantage to all casting action rolls. If any of these are 8 or higher, unless you roll a natural 20, you cause a Minor Miscast, and if you fail, you cause two of them and the spell doesn't work. At 10, unless you roll a natural 20, you suffer a Major Miscast, and if you roll a natural 1, you suffer 2 of them. Remember the corruption system is optional and not recommended for everyone. It is just a way to...add a layer of slow descent into madness, but if it is too much extra to use, it is recommended you simply do not use it. If anything the best way to deal with it, and the suggested way, is for the GM to silently track it from behind the scenes as loosely or fully as they wish, and just inform you of how it effects your character when it becomes relevant.

What are Miscasts?: A Miscast comes in two forms, Minor and Major. Both of these events can still occur even when a spell is cast successfully. How they happen is someone draws to much manna in for a spell weaving, and simply doesn't know what to do with it, has no way to vent it safely, and simply.....releases it in an uncontrolled manner, causing a rippling reactive disturbance in the Aether that can cause random, and sometimes quite dangerous, effects to manifest in the Materium. These events are quite random in their nature, and in what they do. Below the two miscast tables will be provided. Each uses a d100 when triggered and that dictates what happens. At baseline your spell still works if you fail the casting roll, but you suffer a minor miscast. If you roll a natural 1, your spell doesn't work and you suffer a minor miscast.

Minor Miscast Table

d100 roll	Miscast Event: Brief effect description
01-05	Witchsign: Next living creature born within 1 mile is mutated.
06-10	Soured Milk: All milk within 3d100 feet of you sours instantly.
11-15	Blight: Your Wisdom Modifer number of fields within Wisdom Modifier miles suffer blight, all crops rot overnight.
16-20	Soulwax: Your ears clog instantly with a thick wax. You are Deafened until you take an action to clean them.
21-25	Witchlight: You glow with the light of large bonfire, appropriate color to you Order of Magick, lasts 1d10 rounds.
26-30	Fell Whispers: Pass a Wisdom Saving Throw, with Advantage, or gain 1 corruption point (GM should roll influence randomly)
31-35	Rupture: Your eyes, nose and ears all start bleeding profusely. You begin to take 1d10 bleeding
36-40	Soulquake: You get rocked off your feet, you are knocked prone.
41-45	Unfasten: On your person, every knot, buckle, and strap comes undone, which may cause belts, pouches, armor and more to fall.
46-50	Wayward Garb: Your clothing seems to gain a mind of its own, you are now Restrained, DC to escape is equal to your Spell DC.
51-55	Curse of Temperance: All alcohol within 3d100 feet of you goes bad, tasting bitter and foul.
56-60	Souldrain: You gain 1 level of exhaustion, which lasts 1d10 hours.
61-65	Driven to Distraction: If engaged in combat, for the next round, you count as surprised, and lose concentration if you were maintaining it. Otherwise you are startled and unable to concentrate for a few moments (about 6-12 seconds).
66-70	Unholy Visions: Make a Wisdom Saving Throw, as you see a glimpse beyond the Aether, you glimpse into the horrors of the Void. If you fail, you are Blinded for 1d6 rounds. If you succeed, you are only blind for 1 round.
71-75	Cloying Tongue: Suddenly finding yourself barely able to speak, your tongue feeling swollen and unwieldy. All attempts at doing anything requiring you to speak (Casting, conversational skill checks, etc) are at Disadvantage for 1d10 rounds
76-80	The Horror: Glimpsing into the Void through the Aether, something looks back. Make a Wisdom Saving Throw with Disadvantage. If failed, you are Frightened of all magick for 1d10 rounds.
81-85	Curse of Corruption: Gain 1 corruption, from random influence.
86-90	Double Trouble: The effect of your intended spell, despite its range limits, is enacted somewhere random within 1d10 miles.
91-95	Multiplying Misfortune: Roll twice on this table rerolling results of 91-100
96-100	Cascading Chaos: Roll on the Major Miscast Table and use that result instead.

Major Miscast Table

d100 roll	Miscast Event: Brief effect description
01-05	Ghostly Voices: Everyone within 6d10+Your Wisdom Score feet of you hears darkly seductive voices from the Void. All sapient beings in range must roll a Wisdom Saving Throw against your DC or gain 1 corruption (including you).
06-10	Hexeyes: Your eyes turn an unnatural color associated with your Order of Magick for 1d10 hours. While your eyes are like this, you are Blinded and it cannot be resolved by an means other than Greater Restoration or other curse breaking methods.
11-15	Aethyric Shock: You take 1d10 damage as appropriate to your element tied to your Order, and no resistances or immunities apply. Also make a Constitution Saving Throw, with Advantage. If failed, you are Stunned for 1 round.
16-20	Deathwalker: Your footsteps leave death in their wake. For the next 1d10 minutes, anywhere you walk, all plant life withers and dies.
21-25	Intestinal Rebellion: Your bowels move uncontrollably and you soil yourself. You are Sickened and gain 2 levels of Exhaustion that cannot be cleansed until you clean yourself up, or by magickal means.
26-30	Soulfire: You burst into unholy flames of a brilliant color associated with your Order of Magick. You are now on fire.
31-35	Speak in Tongues: You gabble unintelligibly for 1d10 rounds. During this time you cannot make Casting or Pray actions, nor speak in any way that anyone can understand.
36-40	Swarmed: You are engaged by a swarm of Aethyric creatures as appropriate for your lore (GM Discretion, but think like Rats for Onyx, Crows for Amethyst, Fire ants for Ruby, etc. Thematically appropriate.) After 1d10 rounds if not destroyed, the swarm simply fades away.
41-45	Ragdoll: You are flung randomly in a direction 3d10 feet, taking appropriate fall damage+1d10 when you hit the ground and are Prone.
46-50	Limb Frozen: One limb (decided at random) is frozen in place for 1d10 hours. It is considered useless as if amputated.
51-55	Darkling Sight: You lose the benefit of Aether-Sight for 1d10 hours. Casting actions are at a Disadvantage during this time.
56-60	Chaotic Foresight: Gain 1d4 Luck Points, as if the Luck Feat. But they disappear forever at tend of session. Every time you use one, gain 1 corruption point (GM decides).
61-65	Levitation: You are lifted by the currents of manna against your will, 3d10 feet into the air for 1d10 minutes. You can be forcibly moved but if left alone, will return to that height off the ground Once it ends, you fall and take appropriate fall damage.
66-70	Regurgitation: You spew uncontrollably, vomitting more than your body can possible contain. You are Stunned for 1d10 rounds.
71-75	Mannaquake: All creatures (and yourself) within 3d100 feet must make an Athletics Test at Disadvantage or be tossed Prone.
76-80	Foul Enfeeblement: Gain 1 corruption point, collapse Prone, and gain 2 levels of Exhaustion.
81-85	Voices of Madness: Gain 1 mental condition/insanity.
86-90	Gift of Mutation: You suffer a physical mutation.
91-95	Aethyric Feedback: Everyone withing 2d10 feet of you, friend and foe alike, suffer 1d12 damage of each element (all eight Orders) damage, and are knocked Prone. If there are no targets in range, the manna has nowhere to vent, so you immediately drop to 0 hit points and fail two death saves, as your body is brutalized by this storm of elemental energy within you.
96-99	Possession: Your soul may remain, but you are imprisoned in your own body, possessed by a Terror of the Void, one tied to the corrupting influence you have wracked up the most corruption in.
100	Rift in Reality: You are utterly consumed by the magick, making a Consitution Saving throw. Should you fail, you are just dead. Should you succeed, you are unconscious, but being used to keep the Void Portal that tears open where you stood stable. You have disadvantage to all Death Saves, and DO NOT wake up if you succeed three so long as you are within 100 feet of the tear in reality, as it keeps feeding on you to stay stable. A Void Incursion begins, 1d10 Terrors and 2d10 Horrors of the corrupting influence you had the most corruption in pouring out immediately. If you had a Corruption of 7 or more, a Nightmare leads them. If you die or are brought outside of 100 foot radius of the portal, it collapses and fails. Each round it is open 1d4 more Horrors come forth.

Simplified Rules: Perhaps you want the essence of this, but don't want to deal with all crunch of it. A simple system that can also work, and is notably less harsh, is simply a 5 or less and natural 1 set up. Any time an arcane caster wishes to cast a spell, you simply roll a d20 (Advantage and Disadvantage are up to you) and you roll a 2-5 the spell works but they suffer a Minor Miscast. If you roll a 1, you can make them make a Saving Throw for their relevant Casting Ability against their own Spell DC. If they pass, the spell doesn't happen and they still suffer a Minor Miscast. If they fail, they suffer a Major Miscast.