Crafting Magic Items: Draft Rule

Following up on Saturday's post on Crafting Magic Items, here's the draft rule. Any thoughts, suggestions, etc. are welcome!

A magic user attempting to create a magic item must roll 12 or better on a d20, modified as follows:
-1 per spellcasting level/2 (round down)
+1 per spell level
-2 Scrolls, potions, single use items (runes, charms, etc.)
+0 Items with charges (wands, staffs, etc.)
+2 for permanent items (rings, figurines of wonder, bags of holding, etc.)
+2 per plus (Sword +1, Shield +2, Ring of Protection +1)
+1 per plus ammo or specific creature (Sword +1 +3 vs dragons, Arrows +1)
-1 per +10% spent, cumulative (i.e. 100gp base, +10gp, +11gp, +12gp, etc. )

Magic item creators gain XP for the creation attempt based on the cost of the item, regardless of the result (unless otherwise noted). Only gold spent on the base cost of the item contributes to XP.
An unmodified roll of 1 always fails
For all failures, roll on the below chart.

Failed Magic Item Creation Results
Failure doesn’t necessarily mean that you don’t end up with a magic item…
Roll a 1d12, add the difference between the target number and the failed roll. Double that if you rolled a 1. (i.e. target is 8, roll was 2, add 6 to d12. if roll was 1 add 14!)

2. The magic failed to bind. If item is attempted again, base cost is ½ normal.
3. The magic bound in a useless fashion. Still detects as magic, does nothing magical.
4. The magic warped the item into uselessness.
5. Magic Backlash! -1 to Int
6. Opened Mind +1 Int, -2 Wis
7. Life drain, item created, wizard loses 1d6 Con or Strength
8. Gained the attention of an extraplanar being. It doesn’t like you.
9. Gain no XP from the attempt.
10. The item now drains magic from other nearby magic items to power itself. If it is especially hungry, i.e. has gone years without feeding, it may attempt to absorb spells cast near by or even the magic from magical creatures.
11. He contracted a magical wasting illness. Save vs. poison to avoid contracting it if you encounter him; if infected, save vs. poison once per week or lose 1 point of Constitution.
12. The item is overpowered and has a 75% chance to create a feedback loop when used. The Feedback loop treats the magic as 1 level higher but also affects the user (if offensive) or the closest enemy in proximity (if defensive).
13. It does the opposite of what it was intended. Offensive magic becomes defensive, healing hurts, etc.
14. The item is either underpowered or over powered. If it's effect was intended to affect a single person, it's now an area of effect (10' R). If it was intended to affect an area, it now only affects a single person.
15. The wizard can never again cast the spell (or a random spell) that was being used in the item's creation.
16. The item works, but it actively draws electrical energy toward it. Lots of static shocks, big ones if outside during a storm.
17. The item grows eight arachnid legs and acts as a monster with 1HD per spell level. It has all power(s) intended for the item.
18. The first recipient of the object's effect becomes imbued with the power naturally. If offensive, it may be used once per day. If defensive, it may be used for 1 minute per character level.
19. The item is ripped from this reality, leaving a hole into another. The hole will last 1 day per use or charge, or forever if a permanent item.
20. The item works but is dangerously unstable. After each use the referee rolls 1d20; on a 20 it explodes spectacularly (1d6 damage per level of spell in the enchantment to all in 20' radius, save for half).
21. Rather than creating the spell effect as desired, the item creates a short lived "spell elemental". These elementals have a number of HD equal to the spell level and their attacks mirror the normal spell effect. While independent from the item's user, offensive effects tend to be hostile to everyone while defensive effects tend to be protective of the user. They survive for 1d6 rounds before they die of "old age".
22. The item is intelligent, and loathes the caster with the power of a thousand suns. The imbued power will not work for the caster, but works x2 against him. The item will struggle to control it's wielder and if it succeeds will direct them to attack the caster.
23. The spell effect become entangled with another random school/spell. A fireball may animate the dead, a shield may be accompanied by a strange phantasmal force, etc.
24. Every time the item is used it summons a demon hostile to the item's user.
25. Every time the item is used or donned, it summons a demon (never a succubus) amorous to the item's user.
26. A person using the item cannot sleep in the next 24 hours. If worn or carried, the character is completely unable to sleep. They get no rest for spell or healing purposes and every day without sleep gains a cumulative penalty (-1 for day 1, -2 for day 2, etc) to all rolls made.
27. The spell went in fine, or at least it seems that way. Any time the item is used roll on the wild magic table
28. Use of the item slowly transforms the user into a creature based on the function of the item. A wand of fire will slowly turn the user into a fire elemental. A ring of invisibility slowly turns the user into an invisible stalker. The down side is that the creature only has HD equal to half the user's level. Each odd use of the item grants the user an ability of the creature. Each even use of the item grants the user a flaw or vulnerability. When all flaws and vulnerabilities are gained, the user loses a level with every even use until they reach 1/2 their original level. 
29. Is now trapped inside the item. He has to replace himself to get out.
30. An arm or leg (1d4) is now imbued instead and the magic is leaking. In 1d6 weeks, it will completely drain out, leaving the extremity a withered, useless husk. If the intended item had a number of uses, they are still available but each use hastens the wither effect by 1 day.

Examples:
(item costs are based on Robert Conley’s Magic Item Creation Costs PDF):

MU1 creating a Scroll of Sleep (Base Cost 100gp)
Base 12
+1 (First Level Spell)
-2 (Scroll)
-7 (extra gold (94.87gp))
d20 roll needed = 4+
Total Cost = 194.87gp

MU6 creating a short sword +1 +3 vs goblinkin w/ detect goblins 60’ (Base Cost 1600gp)
Base 12
+2 (2nd level detect spell equivilant)
+2 (+1 bonus)
+3 (+3 vs goblins)
-3 (MU level)
-4 (extra gold (742.56gp)
d20 roll needed =12+
Total Cost = 2342.56gp

MU5 creating a Wand of Charm Person w/10 charges (Base Cost 2,000gp)
Base 12
+1 (First level spell)
-2 (MU level)
-2 (extra gold (420gp))
d20 roll needed = 9+
Total Cost = 2,420gp

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Big thanks to Wayne Rossi, A. Miles Davis, Duncan McPhedran, Reece Carter, Sean Holland, and Seth Clayton for their help with the failure chart.