Expanded Spellcasting Rules
Impromptu Casting
When a caster is in a tight spot, they may wish to cast a spell available to them that they did not have the foresight to prepare. While it tends to be discouraged in classical training, it is possible to cast a spell without preparing it first, but it comes with the drawback of having less control over the magic you wield.
These rules allow casters to attempt to cast a spell that is available to you, but is not prepared. To do so, you must first spend an action readying the spell. You must be holding a spellcasting focus to do this. Alternatively, if you are a Wizard, you can be holding an item bearing the spell formula. Most often this is a spellbook, but other items can be used, such as a weapon with the formula engraved onto it.
Having a spell readied requires concentration, as if concentrating on a spell. See "Chapter 10: Spellcasting" in the Player's Handbook for rules regarding concentration. You lose your readied spell when you next cast a spell of 1st leevel or higher, or after 1 minute.
As long as a spell is readied, you can cast it, but doing so comes with additional risk. When you cast a readied spell, roll a d20 and add the level of the spell. If the result is greater than 10 roll on the Magical Mishap table. If the result is greater than 20, roll twice.
Magical Mishaps
When a spellcaster is reckless in their use of magic, they can lose control of it, creating random effects. When this happens roll on either the Magical Mishap table to determine the effect. If that effect is a spell that normally requires concentration, it doesn't require concentration in this case; the spell lasts for its full duration unless otherwise stated.
References
- Monster Manual page 207.
- Dungeon Master's Guide page 259.
- Dungeon Master's Guide page 272.
Minor Mishap
| d100 | Effect |
|---|---|
| 1-3 | For the next 24 hours you leave glowing illusory footprints that last for 1 hour. |
| 4-5 | Each creature within 15 feet of you (including yourself) takes 1d8 force damage per level of the spell as magical energy crackles off you. |
| 6-7 | You take 1d6 necrotic damage per level of the spell and bleed from your eyes, nose and ears. |
| 8-9 | For the next minute, you are blinded. |
| 10-12 | You are frightened of the nearest creature until the end of your next turn. |
| 13-14 | You age 1d10 years. |
| 15-16 | You can't speak for the next minute. Whenever you try, a thick black fluid seeps out of your mouth. |
| 17-18 | You itch all over. At the start of each of your turns, make a DC 10 Constitution saving throw. On a failed save, you spend your turn scratching into yourself and take 1 damage. This effect lasts for 1 minute. |
| 19-20 | Your bones feel weak. For the next minute, you are vulnerable to bludgeoning damage. |
| 21-22 | You cast gaseous form on yourself. |
| 23-25 | The spell has no meaningful effect, but a minor sensory effect may occur as determined by the DM. The spell slot and components are still expended. |
| 26-27 | One nonmagical item on your person or that you are wearing crumbles to dust. |
| 28-30 | For the next minute, any flammable object you touch that isn't being worn or carried by another creature bursts into flame. |
| 31-32 | You cast summon lesser demons at your location. The spell ends after 1 minute. |
| 33-34 | For the next 2d6 days, horrid pustules grow on your face giving you disadvantage on all Charisma checks. A remove curse spell can end this effect. |
| 35-36 | The next creature you kill using magic instantly reanimates with half of its maximum hit points. It's type becomes undead, and all of it's ability scores are decreased by 2. |
| 37-39 | The spell targets the wrong creature or area, as determined by the DM. |
| 40-42 | You feel a bead of residual energy inside you that hurts you if not released. You take 1d4 force damage at the start of each of your turns for 1 minute or until you cast a spell of 1st-level or higher. |
| 43-44 | You cast polymorph on yourself. If you fail the saving throw, you turn into a sheep for the spell's duration. |
| 45-46 | You gain the curse of lycanthropy1. |
| 47-48 | The next time take a long rest, you recover half the hit point you would normally as you are beset with horrible nightmares or visions. |
| d100 | Effect |
|---|---|
| 49-51 | You are restrained for 1 minute as black tentacles bind you in place. You can escape by using your action to make a DC 15 Strength (Athletics) or Dexterity (Acrobatics) ability check. |
| 52-54 | You gain a level of exhaustion. |
| 55-56 | You cast confusion centered on yourself. |
| 57-58 | When you next use a spellcasting focus, it glows bright white and becomes painfully hot. At the start of your next turn, it explodes, casting fireball as a 3rd-level spell at its location as it does so. |
| 59-60 | A hostile poltergeist is summoned within 30 feet of you. It disappears after 10 minutes or when it drops to 0 hit points. |
| 61-62 | You cast grease centered on yourself. |
| 63-65 | As you cast the spell you release a loud bang. You take 1d4 thunder damage, and you are deafened for 1 minute. The noise can be heard 100 feet away. |
| 66-67 | You feel wave of nausea overcome you. You take 1d4 poison damage and must spend your next turn vomiting. Additionally, you are poisoned for 1 hour. |
| 68-70 | Minimize the damage of the next damaging spell you cast within the next minute. |
| 71-72 | The spell appears to fail, but will take effect 1d4 rounds after casting. |
| 73-75 | The spell fails, causing no effect. |
| 76-77 | An earth, air, fire, or water elemental under control of the DM is conjured in an unoccupied space within 60 feet of you, and disappears after 10 minutes or when it drops to 0 hit points. |
| 78-80 | You cast earth tremor as a 1st-level spell. You must also make a saving throw against the effect. |
| 81-82 | Your flesh turns to stone and you are petrified until the end of your next turn. |
| 83-84 | You cast enlarge/reduce on yourself, shrinking yourself on a failed save. |
| 85-87 | For the next 24 hours you lose proficiency with one random skill you are proficient in. |
| 88-89 | You forget everything that has happened in the last 1d10 minutes. |
| 90-91 | The next object you touch is animated, as in the animate objects spell. It is hostile to you. |
| 92-93 | You turn into a potted plant until the start of your next turn. While a plant, you are incapacitated and have vulnerability to all damage. If you drop to 0 hit points, your pot breaks and your form reverts. |
| 94-95 | You cast otiluke's resilient sphere on yourself. |
| 96-98 | Something snaps, and you gain a madness effect2. Roll a d6. On a 4-6, roll on the Short-Term Madness table. On a 2-3, roll on the Long-Term Madness table. On a 1, roll on the Indefinite Madness table. |
| 99-100 | A price is paid. Roll on the Lingering Injury table3. |
Credits
Document and contents by Dylan Richards. Reddit: u/Altavus Blogger: Decision Paralysis Twitter: @DillTheHerb
All work is presented under the Open Game License.
Source Material
This work is inspired by Logan Knight's "Do Not Take Me For Some Turner Of Cheap Tricks" post on their blog, Last Gasp
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