Magical Conditions of Limbo

It doesn't take a bloody genius to foretell that as unpredictable as LImbo is, spellcasting there must be chaotic. This is especially true of spells cast within the primal soup where the environment is usually changing even, as a spell is being cast. Solid terrain maintained by a concious mind provides a somewhat more stable platform for magic use, but even there spells frequently break loose from a cutter's control.
As a result, there's a general rule that applies to all spellcasting by wizards and other casters on the plane. In order to cast a spell of any school anywhere within the plane of Limbo, a spellcaster first has to make a skill check with his spellcasting attribute, the DC of the check is 10 + level of the spell being cast. If the roll is failed, the spell slot is wasted and no spell is cast: the chaotic nature of the plane has prevented the spell's effect from taking place. The poor sod of a caster just stands there looking sheepish. In addition, if the failed spell was being cast within the primal soup of chaos, a wild magic surge (see wild magic sorcerers) automatically occurs. If, instead, it was being cast on stable terrain, roll a spellcasting check against a DC of 12 + level of the spell cast, the spell fails on a unsuccesfull skill check and causes a wild magic surge.
Other special conditions vary by spell, as follow.

Determining how a spell is effected

It would be nice for a cutter if a spell would just adjust to the plane depending on their school but that is, regrettably, not the case. This is especially often the case for spells of the evocation or conjuration school, or at least here on Limbo. A evocation spell that deals with energys that aren't of the elemental sort are often considered transmutation for the case of effects, an example would be the darkness spell, as it creates new "matter" so to say and isn't elemental in nature. So a darkness spell would be affected as any transmutation spell.
The same's true for conjuration, any conjurations that don't deal with summoning something that's alive will most likely fall under transmutation.
Of course some schools and spells are not effected besides the general danger of the spell failing for a wild magic surge. Necromancy spells or the evocation spells of the healing sort would come to mind.

Transmutation

Casting transmutation school spells on Limbo can be incredibly dangerous! Because conditions are so fluid on the plane, the final product of the alteration may be far from what the caster intended. There have been cases of berks trying to polymorph an attacking slaad into a newt, for instance, and getting a green dragon instead!
Whenever a character in Limbo attempts a spell that calls matter into being or changes its shape or form, if the spell goes off successfully (the spell casting attribute check above is passed), roll 1d100 and consult the following table to determine the result. Add the spell's level to the roll, but subtract the caster's level. (Modest spells cast by experts are somewhat safer than a tyro's toughest spells.)

% roll	Effect
<=20	No special effect
21-40	Slightly modified appearance
41-60	Slightly modified appearance and properties
61-80	Moderately modified appearance and properties
81+	Highly modified appearance and properties

The exact result in each case is left to the DM's invention, but let the spellcaster's intention be a guide to the final result. Imagine that as the caster struggles to control the spell, his subconcious mind provides an alternate shape somehow related to the intended one. In the example above, for instance, a dragon and a newt are both reptiles. With that in mind:
A slightly modified appearance means that the spell functions as intended: its effects merely looks a bit strange. Pyrotechnics might have an unexpected tint to it, for example.
Slightly modified appearance and properties means that the spell effect functions mainly as intended, though there are some minor variences. A wizard undergoing Tenser's transformation might actually appear troll-like and grow claws, adding one point to any damage done by unarmed attacks: or heat metal, may make a cutter feel cold and wet instead, dealing cold damage.
Moderately modified appearance and properties means the spell effect has some marked differences from what is expected. For example, flesh to stone might actually turn flesh to cactus.
Highly modified appearance and properties means the spell runs wild, often playing upon the caster's secret fears. DM fiendsihness is encouraged in devising the specific results.

Conjuration

First of all, like with every plane, summoning spells can only summon from the plane you are on, so you'll have a hard time summoning any celestials here in Limbo. But it's also worth mentioning that the powers here tend to respond to wish and Limited Wish very frivolously. Souls casting these spells on LImbo are really taking their chances.
Sometimes wizards who've lost a familiar come to Limbo to seek a new one with the find familiar spell. It's not the sort of thing most low-level casters are up to, what with the difficulty of traveling to the plane in the first place and the inherent dangers once a basher gets there, let alone the chance of the spell just dissipating into chaos. But assuming the spell goes off successfully, the caster is very likely to have a choice of more than one familiar to choose from, assuming she can reach it in time.
When the spell is cast, the wizard senses the presence of 1d4 possible familiars instead of choosing from the list. These familiars are however special in comparison to the normal familiars, what makes them special is left up to the DM. Examples could range from such things as exceptionally large, tough, and intelligent versions of normal familiars, to a huge insect, to a highly magical creature such as a wyrmling dragon or mephit. However, familiars of increased intelligence will all tend to chaotic alignments as lawful creatures are very rare on Limbo (though aby that are encountered will likely be very glad to become a familiar, if it means being transported from the plane).
Due to Limbo's nature, potential familiars usually cannot come to the caster. Rather, the caster must choose one of them and froceed toward it. The first creature is the closests, 1-6 hours of travel away at walking speed. If there is a second, it is 2-12 hours away, the third 3-18 hours away, and so on. The wizard must choose which creature to travel toward: the others are immediately lost from the spell. The caster then begins walking toward the chosen creature, continuing to chant and keeping the brazier used in the spell burning. If the wizard reaches the chosen creature (within a time limit of 4d6 hours, which the DM secretly rolls for), it becomes her familiar. Otherwise no familiar is gained.

Divination

As ought to be expected by any berk with any understanding of Limbo at all, divinations are really dificult on this plane. Besides the normal problems of casting spells in general, the plane's tumultuous nature interferes with the reading of these spell's portents. The caster makes a wisdom saving throw against DC 14 + level of the spell. If the saving throw is failed, the spell's results are so chaotic that the caster gains no information.

Illusion

Now, it's true that raw chaos matter is so anarchic that it often disrupts the magical forces of spells. But it's also true that once a spell is actually underway, chaos matter is malleable enough that it often follows the spell's form, extending the magical effect. In the case of the Illusion school, this means that things that aren't normally real have a chance of becoming real. So each time a cutter on Limbo casts a spell from his school, there is a 10% chance of the effect becoming fully, permanently real. (Well, at least as permanent as anything can be on Limbo.)

Wild Magic

Remember that spells of all schools have a chance of causing a wild surge in Limbo, if the caster rolls a natural 20 on a d20 (also causing the spell to fail). Besides this chance, if a wild magic sorcerer casts a spell it also incurs a chance of a wild surge accompanying a succesful spell (the caster passed the spellcasting test). Whenever a wild magic sorcerer succesfully casts a spell, the spell is automatically accompanied by a wild magic surge, however, instead of rolling 1d10 the cutter rolls another 1d100 and picks the dice he likes more. In addition they can choose to add or subtract their charisma modifier to the result.
Additionally, spells that are of chaotic nature and involve randomly determined results, like chaos bolt or confusion, are enhanced on Limbo. The spell cast will always act as if cast at a higher level, so a chaos bolt cast at 2nd level becomes a chaos bolt cast at 3rd level. In addition to that, all spell attack rolls of these spells are increased by 1 as well as the saving throw DC of these spells.
All this means one thing, in other words, only an addle-cove of a wild mage comes to Limbo!

Elemental

Scholars scratch their heads and mumble when asked why Limbo is so elemental in its nature. See, Limbo's an Outer Plane, and the elemental planes are Inner Planes, so it's strange that Limbo would act so much like a mixture of raw earth, air, fire, and water. 'Course, scholars scratch their head and mumble when asked why any of the Outer Planes have any sort of elements, rather than being mostly immaterial, like the Astral Plane.
But whatever the reason, Limbo seems very elemental. And because of that, spells that use the raw elements - if they don't just fizzle - are quite a bit more powerful than elsewhere in creation. In each case, the duration and area of effect of the spell is doubled. If the spell is normally instantanious, it lasts for 1d6 rounds. If its area of effects is normally one target, it affects an area of 1d10ft in radius.
In addition, all elemental spells are cast at one level higher, so a Fireball cast at 3rd level becomes a Fireball of 4th level. Also, all spell attack rolls and saving throw DC are increased by 1.
It's extremely important to keep in mind too that elementals conjured on this plane are exceptionally difficult to control. Because their nature is that of this most chaotic of planes, they interpret their conjurer's instructions as loosely as possible. And to make matters worse, their attention span is extremely short, which prevents a conjurer from giving them directions with all the "loopholes" covered. So a mage who conjures an elemental on Limbo is either very desperate or a total addle-cove.

Spell Keys

Spell keys on Limbo are typically used to avoid the chance of a spell dissipating, and possibly resulting in a wild surge, the primary problem with spellcasting on the plane. (In other words, most spell keys just mean a basher doesn't have to make an Intelligence check to make a spell go off right.) 'Course, some can be used to circumvent other problems, such as the difficulty involved in summoning things from the Inner Planes.
Keys here fall into two categories. The first involves the essence of change, the second the essence of balance. Keys involving change are most useful for spells of the schools of Transmutation, Enchantment and Illusion. Those involving balance typically apply to spells of the Abjuration, Conjuration and Evocation schools.
One example of a changeble key is a blown smoke ring. As it moves away from the person who created it, it grows both larger and more tenuous, finally to fade away completely. A pinch of salt dissolving in a few drops of water is another example. Purists like to point out that in each case, the key isn't the physical components themselves. but rather the change they go through. So the spell for which the key is intended must be cast as the key is changing. But despite that overly fine distinction, the physical components are still consumed in the casting.
Examples of balance-related spells include such things as a spinning coin or an ornamental dagger poised on a fingertip. For more powerful keys, an element of risked destruction can be helpful, as in holding an egg or fragile glass sphere aloft, balanced on the tip of a staff.
Unlike most other planes, spell keys are a matter of constant change of Limbo. There's no way of noting down what worked one time, passing the trick along to someone else, and expecting it to work again later. It won't even work twice the same way for the same caster! So using spell keys on Limbo is an issue of insight at the time and place a spell is being cast. To represent this, the DM should call for a spellcasting ability skill check. If that roll is succesful, the caster is able to recognize what sort of thing would be appropiate to serve as a key at the moment. Then, of course, and effort of will can bring the key component or components into existence from the background chaos matter of Limbo (in other words, make a skill check to create it). Obviously, all this ruminating and calling key components into being takes a bit of time and trouble. So a cutter's got to decide wheter or not to take the trouble, depending upon the situation at the time.
Because use of spell keys on Limbo isn't as cut and dried an issue as elsewhere, and because it can become a bit involved, the DM and players should use it as an opportunity for adding some flavor to their storytelling and role-playing. In other words, the purpose of these rules isn't merely to add complication to the mechanics of magic use: rather it's to convey the unusual nature of Limbo, with and eye towards making adventures more exciting.

Power Keys

Compared to powers elsewhere, those in Limbo are fairly open-handed in the awarding of power keys to their clerics. That doesn't mean that they give them out to just anybody, but they take a slightly different approach to deciding who deserves one. See, rather than test their priests for ages before dolling out a key to those that prove faithful, these powers are more apt to give out a key, then watch to see how a cleric uses it. In other words, the award becomes the test. Clerics who prove faithful get to keep their key: the others lose theirs just when they're needing it most. Then again, sometimes Limbo's powers negate a key out of sheer capriciousness. But any berk who can't handle the uncertainty shouldn't be serving a Chaos power in the first place.
Spheres that these powers most often give out keys for include Enchantment, Spells that create stuff, and spells dealing with the Elements. Fenmarel Mestarine makes a slight exception: He's more apt to give out keys for weather spells rather than elemental ones.