Critical spell failures and wild magic in D&D 5E

What the !? I was trying to cast summon ham sandwich...

What ho, Adventurers! Sometimes you want magic to be freewheeling and frivolous. And sometimes you want it to be frightening, dangerous, and unpredictable for everyone involved, especially the spellcaster. 

While the D&D 5e Players Handbook  does include a large D100 chart of wild magic misfire effects, they are not very complimentary to a more gritty campaign. The best example would be the effect if you roll a 41-42 "You turn into a potted plant." I like Douglas Adams as much as the next guy, but this isn't really going to reinforce any feelings of dread and menace in my players.

For my upcoming campaign, I want every spell cast to have a chance of horrible consequences. Magic is a dangerous thing, and those who use it often wind up twisted creatures to be feared and loathed. Thus for every spell cast, even automatic effect spells with no roll such as the ubiquitous Light spell, you roll a d20. If you roll a 1, that is a critical failure, and you then roll on a table for effects.

After much google searching and rpg system scouring, I have settled on using the spell corruption tables from Dungeon Crawl Classics RPG. Like most of the rules in that excellent game, they are highly thematic and very well written. There are three levels of corruption from failed magic: minor, major, and greater. In DCC RPG the table that you use is based on the spell cast. We will be using it differently.

In this variant, it will be an exploding dice roll, where a result below 1 means you move to the next table. Roll badly enough on the minor table and you go to the major table. Roll badly enough on that table, and you roll on the greater table. Roll badly on the greater table and you might be rolling up a new character. Using this system, even with casting that simple Light spell, if you blow enough rolls you could wind up having your head transform into that of an insect, or having your flesh rot and fall away in chunks, or having your character wink out of existence entirely! However, this varaint will be using a d20 rather than a d10, so the most likely outcome of a spell failure will simply be falling unconscious for 1d6 hours unless woken forcibly. This system can also help explain why high level magic users don't go around casting world changing magic all the time. A critical failure on a ninth level spell would be likely to have some very serious negative effects! 

The formula used will this: 

roll 1d20 - spell level (cantrips are level 0)

For those who have not yet purchased the DCC RPG core rulebook, the charts are below, with slight adjustments made to port it to D&D 5e, a fatal failure added as the worst roll on the greater corruption table, and also added the exploding dice roll feature. The details are all otherwise the same. I cannot reccomend purchasing this book enough! Even if you never play it, the ideas in it and the accompanying art are spectacular.

Minor Corruption

Below 1 - Roll on Major corruption chart

1 - Character develops horrid pustules on his face. These pustules do not heal and impose a -1 penalty to social charisma ability checks.

2 -  Character’s skin on one random portion of his body appears to melt. Like wax, it flows and reforms into odd puddles and shapes. This is an ongoing, constant motion that itches constantly and repulses others. Determine location randomly (1d6): (1) face; (2) arms; (3) legs; (4) torso; (5) hands; (6) feet.

3 - One of the character’s legs grows 1d6”. Character now walks with an odd gait.

4 - Eyes affected. Roll 1d4: (1) eyes glow with unearthly color; (2) eyes gain light sensitivity (-1 to all rolls in daylight); (3) character gains infravision (sees heat signatures at range of 100’); (4) eyes become large and unblinking, like a fish.

5 - Character develops painful lesions on his chest and legs and open sores on his hands and feet that do not heal.

6 - Ears mutate. Roll 1d5: (1) ears become pointed; (2) ears fall off (character still hears normally); (3) ears enlarge and look like an elephant’s; (4) ears elongate and look like a donkey’s (character also gains braying laugh); (5) ears shrivel and fold back.

7 - Chills. Character shakes constantly and cannot remain quiet due to chattering teeth.

8 - Character’s facial appearance is permanently disfigured according to the magic that was summoned. If fire magic was used, his eyebrows are scorched and his skin glows red; if cold magic was used, his skin is pasty white and his lips are blue. If ambiguous magic was used, his appearance grows gaunt and he permanently loses 5 pounds.

9 - Character’s hair is suffused with dark energy. Roll 1d4: (1) hair turns bone white; (2) hair turns pitch black; (3) hair falls out completely; (4) hair sticks straight up.

10+ - Character passes out. He is unconscious for 1d6 hours or until awakened by vigorous means

Major Corruption

Below 1 - Roll on Greater corruption chart

1 - Febrile. Character slowly weakens over 1d4 months, suffering a -1 penalty to Strength for each month.

2 - A duplicate of the character’s face grows on his back. It looks just like his normal face. The eyes, nose, and mouth can be operated independently.

3 - Consumption. Character’s body feeds on its own mass. Character loses 2d10 pounds in one month and suffers a -1 penalty to Constitution.

4 - Corpulence. Character gains 6d12 pounds in one month. The weight gain imposes a -1 penalty to Dexterity, and the character’s speed is reduced by 5’.

5 - Character crackles with energy of a type associated with the spells he most commonly casts. The energy could manifest as flames, lightning, cold waves, etc.

6 - Character’s height changes by 1d20-10 inches. There is no change in weight; the character’s body grows

thin and tall or short and fat.

7 - Demonic taint. Roll 1d3: (1) character’s fingers elongate into claws, and he gains an attack for 1d6 damage; (2) character’s feet transform into cloven hoofs; (3) character’s legs become goat-like.

8 - Character’s tongue forks and his nostrils narrow to slits. The character is able to smell with his tongue like a snake.

9 -  Small horns grow on the character’s forehead. This appears as a ridge-like, simian forehead for the first month; then buds for the second month; goat horns after the third month; and finally, bull horns after six months.

10+ Character’s skin changes to an unearthly shade. Roll 1d8: (1) albino; (2) pitch black; (3) clear; (4) shimmering quality; (5) deep blue; (6) malevolent yellow; (7) ashen and pallid; (8) texture and color of fishy scales; (9) thick bear-like fur; (10) reptilian scales.

Greater Corruption

Below 1 - The Character ceases to exist. DM fiat on how this happens. Maybe they simply wink out of existence, maybe they explode. 

1 - A sliver of soul energy is claimed by a demon lord. Character experiences unearthly pain, suffering 3d6 damage, a permanent -2 penalty to all ability scores, and an additional -2 penalty to Luck.

2 - Decay. Character’s flesh falls off in zombie-like chunks. Character loses 1d4 hp per day. Only magical healing can stave off the decay.

3 - Character’s head becomes bestial in a painful overnight transformation. Roll 1d6: (1) snake; (2) goat; (3) bull; (4) rat; (5) insect; (6) fish.

4 - Character’s limbs are replaced by suckered tentacles. One limb is replaced at random each month for four months. At the end of four months, it is impossible to hide the character’s inhuman nature.

5 - Small tentacles grow around the character’s mouth and ears. The tentacles are maggot-sized at first, but grow at rate of 1” per month to a mature length of 12”.

6 - Third eye. Roll 1d4 for location: (1) middle of forehead; (2) palm of hand; (3) chest; (4) back of head.

7 - Fingers on one hand fuse while the thumb enlarges. After one week, the hand has transformed into a crab claw. Character gains a natural attack for 1d6 damage and can no longer grasp normal weapons and objects.

8 - Character grows a beak in place of his mouth. Transformation starts as a puckering of the lips that slowly turns into a full-fledged bird or squid beak over the next 1d12 months. Character gains a bite attack for 1d3 damage.

9 - Bodily transformation. Roll 1d6: (1) character grows scales across his entire body; (2) character grows gills; (3) character sprouts feathers; (4) character develops webbed toes and feet.

10+ Character grows a tail over 1d6 days. Roll 1d6: (1) scorpion tail that can attack for 1d4 damage plus poison (DC 10 Fort save or target loses 1d4 Str permanently); (2) scaly snake tail; (3) forked demon tail (grants +1 Dexterity); (4) fleshy tail ending in a useable third hand; (5) fused cartilaginous links ending in spiked stump that can attack for 1d6 damage; (6) bushy horse’s tail. 

Any thoughts or comments are appreciated!