Your chaos burst is:
First things first!
This list describes 10,000 Chaos Bursts, which may be thought of as eruptions of disorder resulting from poorly controlled magic use. The reader is encouraged to substitute more a mellifluous term in place of ìChaos Burstî if so inclined, but thatís what Iím calling them here.
Why do Chaos Bursts happen?
Some would suggest that casting a spell is analogous to going to a faucet for a drink of water. A conventional mage is like a normal person. He holds his glass beneath the spigot, turns on the tap, fills his glass to the desired level, and turns off the tap. Simple, efficient, and orderly. However, the wild mage doesn't work that way. Instead, he smashes the spigot with a hammer, tries to catch as much water as he wants in his glass, and then tries to reseal the ruptured faucet. Complicated, inefficient, and chaotic. And very likely to get the wild mage soaked in the process. So it is with magic. Instead of opening a precise channel for magical energy, the wild mage tears a gaping hole in reality and hopes to get a particular effect. If he can reseal the hole, great. If not, the result is a Chaos Burst.
What happened to the spell I tried to cast?
In the previous edition I suggested that the intended spell be allowed to function unless directly contradicted by the Burst. I now feel this approach to be flawed and propose an alternative: the chance that a spell succeeds despite a Burst is equal to 10% per caster level minus 5% per level of the spell. Thus a 5th level mage who triggers a Burst when casting fireball has a 35% (that is, (5 x 10) - (3 x 5)) chance to succeed. Otherwise, the spell fails and is lost from memory. Feel free to devise similar methods as you see fit.
Can conventional mages cause Chaos Bursts?
Sure! In addition to Wild Magic regions, normal mages can cause Bursts if they are disrupted during the casting of a normal spell. Though unlikely at low levels, higher-power spells can wreak havoc if not properly cast. To represent this, consider that a miscast spell has a percent chance equal to the square of one plus its level to cause a Burst. That is, a 1st level spell has a 4% (1+1)² chance, but a 9th level spell has a 100% (9+1)² chance. This can be modified by the mageís level or some similar value, as determined by the GM.
The description didn't give a duration. How long does the effect last?
In general, if no duration is specified, then a Burst should be considered permanent until dispelled. Alternatively, it may be appropriate for a Burst to persist for as long as the intended spell would have done, or one round per caster levelówhichever is greater. A third possibility is to roll dice to determine the Burstís duration in turns, hours, days, weeks, or whatever. Yet another option is to assume that the Burst will last until some apparently random condition is met, (a brief list of possible conditions is provided at the end of this document). However, if a Burst has an explicit duration, then it should be assumed that nothing short of divine intervention or a full Wish can cancel the effect before that time. Similarly, if a Burst has an instantaneous duration but a permanent effect, such as 1d10 of the targetís fingers vanishing, then the effect can't be Dispelled per se; the target might be Healed, but there is no lingering magical effect to Dispel, so other remedies must be sought. As in the previous edition, any effort to dispel a Burst should be considered at least as difficult as an attempt to dispel magic cast by a mage twice the level of the caster who triggered the Burst. Also, it must be noted that many Bursts produce a beneficial effect in exchange for a heavy price; if the price is negated, then the benefit should also be negated. For example, if the caster becomes immune to disease by cutting off his thumbs, then he should lose that immunity if his thumbs are restored
What about Bursts that just don't make sense?
Effects with invisible or inappropriate results should be kept secret by the GM (at least from the characters) to preserve the mystery and danger of wild magic. If a fish has its feet enlarged or an aerial servant has half of its body turned invisible, the players should be told that nothing seems to happen. Such a statement could as easily mean a red dragon is now stalking the party but is not yet nearby. Likewise, a delayed effect should not be revealed until it occurs; if the caster is to turn into a duck under the next full moon, let him find out when the time comes.
LEGAL DISCLAIMER STUFF
This is a work by the Net Libram of Random Magical Effects v2.00 (copyright by Orrex) and by the Tome of Magic, (copyright 1991 by TSR). No challenge to the status of these or any other copyrights is intended or implied.