Back to thinking about a Chainmail-style Magic Table

Here I am resurrecting an old idea of using rules based on Chainmail to add a spellcasting roll to S&W magic. In the past, I had only gone as far as coming up with the casting table. But here is my rule set with some thought to how rogues fit into the big picture as well as spell failure and fumbles.

Note that using INT to modify the table results only works in the low-bonus world of Swords and Wizardry. Other forms of xD&D may not fare as well. Also, I'm thinking I may need to tweak the Spell Advancement tables to give more spells to prepare for it to work to my happiness.

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PREPARING SPELLS
Each morning, magic-users and rogues may prepare spells as listed on the Spell Advancement table for their classes.

Casting from Scrolls and Spellbooks
Spells on scrolls are treated as prepared spells in this system. A failed casting erases the spell from the scroll, as does copying the spell into a spellbook. Spellbooks may also be used as scrolls in a pinch (if the caster can find the spell in time), though this is best left for very dire circumstances, since it may cause a character to lose his only copy of a spell if he fails in a spell roll.

CASTING SPELLS
To cast a spell, Magic-users and Rogues use the Spellcasting Success table. Magic-users use their character level as their caster level. Rogues use their level/2 (rounded down), which means that level 1 rogues have no ability to cast spells. Characters may add their Intelligence ability bonus to the spellcasting roll.

Spellcasting may have one of three results: Immediate (I) spellcasting allows the spell to take effect right away. Delayed (D) spellcasting means that the spell is delayed until next turn and may be subject to disruption if the spell-caster is struck before the spell takes effect. Negated (N) spellcasting means that the spell fails. If it does, the spell-caster loses the spell and cannot use it again until it is prepared once more the next morning. In addition, the character must make a save or roll on the magical mishap table.

If a spell is disrupted in the middle of casting, save or the spell is negated. If it is negated, save once more or you must roll on the magical mishap table.

TABLE: SPELLCASTING SUCCESS

Spell   Spell               Caster Level
Level   Effect   1-2    3-4     5-6     7-8     9+
-----   ------   ---    ---     ---     ---     ----
1       I        16+    14+     12+     10+     8+
-       D        12+    10+     8+      6+      4+
-       N        11-    9-      7-      5-      3-

2       I        18+    16+     14+     12+     10+
-       D        14+    12+     10+     8+      6+
-       N        13-    11-     9-      7-      5-

3       I        20     18+     16+     14+     12+
-       D        16+    14+     12+     10+     8+
-       N        15-    13-     11-     9-      7-

4       I        n/a    20+     18+     16+     14+
-       D        18+    16+     14+     12+     10+
-       N        17-    15-     13-     11-     9-

5       I        n/a    n/a     20+     18+     16+
-       D        20     18+     16+     14+     12+
-       N        19-    17-     15-     13-     11-

6       I        n/a    n/a     n/a     20+     18+
-       D        n/a    20      18+     16+     14+
-       N        n/a    19-     17-     15-     13-

TABLE: MAGICAL MISHAPS

Roll 1d20 + level of the spell.

d20+LVL     RESULT
-------     -------------------------------
01 - 07     Roll on the minor chaos table.
08 - 10     You are dazed but able to move and defend yourself for one round.
11 - 12     You are stunned and unable to do anything for the next round.
13 - 14     Spell goes wild and strikes random target.
15 - 16     Spell effect is reversed.
17 - 18     You are struck mute for 1d6 rounds.
19 - 20     Your strength is reduced by half for 1d6 hours.
21 - 22     Magical explosion does 1d6 damage to everyone and everything in
           a 30 foot radius.
23 - 24     You take 1d6 damage for every level of the spell.
25+         A dimensional vortex opens to the primal chaos. Save vs. magic or be
           sucked in. Even if you save, take 3d6 damage.

TABLE: MINOR CHAOS

d20 Result
--- -------------------------------
1  The temperature in a 30ft radius becomes unnaturally cold.
2  A wind blows through the area, smelling of sulphur.
3  Plants wilt and milk curdles in a 30ft radius.
4  Ghostly whispering fills the area for 3d6 rounds.
5  Caster's hair turns white for 3d6 days.
6  Animals in a 30ft. radius are spooked, fleeing the area.
7  Caster's eyes glow red (1-3) or lambent green (4-5) for a day.
8  Caster's nose bleeds for 1d6 x 10 minutes.
9  Caster's body covered with sores that go away in 1d3 days.
10  Caster smells of the grave for 1d3 days.
11  Caster takes on pallor of a corpse for 1d3 days.
12  Caster's voice becomes raspy for 1d3 days.
13  Caster's nails turn black for 1d3 days.
14  Caster's hair grows wildly long.
15  Caster's hair falls out.
16  Caster's nails double in length.
17  Caster's veins become visbly dark under his skin.
18  Caster speaks in unfamiliar language for 1d6 rounds.
19  Caster emits slight, unnatural green glow for 2d6 rounds.
20  Referee chooses any effect or makes up his own.