I would say it depends on the magic/spellcasting itself.
The key is in "If you know why you are doing certain things to make a spell work" - but what if not? What if the process is not that clear, and it is not easy to foresee the effect of putting the various spell-parts together. If the result is determined by, say, uttering the magical syllables in a certain order, temporal succession, intonation and while concentrating in a certain way on a certain thing; if not all possible combinations are known (or even all the syllables), then it can be hard to judge what a written spell really does, until one is familiar with it.
If known, then it is fairly easy to identify elements which do not belong to the spell: easiest, when the spell is known, harder, if the caster is familiar with the school of magic, and nigh to impossible if not.
Silly bit aside: a young magic-user has learned a useful spell with a weak tmesis, annoying but nothing critical. As he grew in age and power, somehow he didn't find the time to properly analyze the spell, though probably found some easy workaround. And thus, even after centuries is the spell remembered from the works of this archmage in a deformed, less effective form. (Possibly with a warning, that careless casting may afflict the caster with ______ . :) ) Go to Comment
Something you can seen done, but it does not work for me.
If you read a spell or process, and know why you are doing certain things to make a spell work, then you should be able to spot most of these traps. These are segments of spells that are incongruent with the rest of the spell process. It would be like reading a text on how to make a bird house and having some bomb making material inside.
Now in China, and in many Occult Circles, knowledge and power is always guarded. That is why many martial arts have "secret techniques". These techniques are shrouded in the common exercises that the practioner is supposed to peel away and learn the truth about. Occult elements would shroud spells by including extra lines/ elements that would nulify the spell or make it less effective. So the trap would be the tricks involved.
The tautologos is a very devious trap found in higher level spells. When the caster of this spell invokes the arcane forms and energies his spell is cast without incident. However the next time the mage attempts to cast a spell, even if it is a cantrip, the tautologos spell will activate, and he will try to cast the same high level spell again.
Thus Barnabus the Barmy casts a powerful Summon Planar Demon from the pilfered spellbook of an evil cultist, makes a deal with the demon and then is on his merry way. Two days later he decides to cast a Charm Person spell on a comely young tavern lass, and instead invokes the Three headed Lord of the Fifth Pit, He Who Revels in Disemboweled Foes. Mayhem ensues.
Of course, if the mage doesnt have the spell components to cast the spell, he looses XP equal to the GP value of the spell components, if such are used. If the mage doesnt have the ability to cast a spell of this magnitude again, he takes one large die of damage per difference in spell level. In the above mentioned example, assuming the demon summoning a 6th magnitude power and Barnabus only has a slot left to cast a 3rd magnitude power spell, he is going to take 3 dice of Strain damage from trying to cast beyond his means.
Tautology - needless repetition of an idea, statement, or wordGo to Comment
This is also a fairly insidious tmesian trap spell. Most often placed in dangerous summoning spells, potent scrying spells and elementally aspected spells. This is a smaller spell that can be placed in mid level spells without being noticed. It's effect is fairly simple, as it inverses some aspect of the spell it entraps.
For example, Tamur the Great has stolen a spellbook from Angia the Summoner and decides he is going to use the previously mentioned spell, Summon Planar Demon. This spell has an evil/unholy descriptor and he is ready to start wheeling and dealing with a demon of death and decapitation. Much to his surprise, he ends up summoning Radia, Angelic Defender of Children and Light. Seeing the vile and contemptable owuld be diabolist, the confrontation is sudden and violent.
Other less dramatic examples include altering fire spells to ice spells, turning poison cloud spells into happy cloud spells, and curses into boons.
Enantiodromia - the changing of something into its oppositeGo to Comment
This is the most straightforward and potentially lethal of all of the tmesian spells. All spells involve the concentration of magical energies in a safe manner. The Nocuon actually draws in these magics in a very hazardous manner, channeling them through the vulnerable flesh and bones of the caster causing magical burns. The more powerful the spell, the more signifigant the damage inflicted.
Going back to the 6th magnitude Summon Planar Demon, Luchilde the Insolent decides to cast the spell from a stolen book of a slain rival. He performs the various gestures as dictated by the book and as he invokes the spell after several minutes of chanting he is filled with immeasurable pain. AS the spell is of the 6th magnitude, Luchilde the Insolent takes 6 dice of damage, and with a mage, often weak in health/hit points, this could very well kill him on the spot before the spell is completely cast.
The hardest part for me was to vote as I did. While I don't like to vote this high I couldn't see a reason not to.
As a person who has created so many different forms of magic use in ym Hewdamia system and never been happy with any of them, this is a refresher idea that is perfect. Especially in a high magic environment with many forms of magic available. Not to mention different magic factions, hence the need for spell protection. Kudos Scras... a job well done.
Its hard to lay claim to which effect I like the best... bravo. Go to Comment
Incurion- a rather devious tmiesian enchantment; Incurion is an unusual, highly specific form of psychic enchantment: it causes the caster to 'forget' a specific sound or syllable- the 'object' of the tmiesis. When reading or listening, they will simply not process the object; when speaking or writing, they will skip over it without missing a beat- think 'Fnord' from the Illuminatus! trilogy.
Incurion is a particularly devious tmiesis, in that its effects, by definition, go completely unnoticed by the individual- very often, the object is one not found in the spell the tmiesis is hidden in; rather, the feeling that something isn't right will only begin to dawn on the caster slowly. Spells will fail or misfire; the enchanter will get odd looks in conversation as he skips syllables in his speech- minor annoyances at first, but enough to unnerve or madden the victim.
Must be removed by a second party, as the victim, even if somehow aware of the enchantment's effect, is completely incapable of determining what, precisely, the object is, and what words it's found in. Easily detected by asking the victim to say a word containing the object- useful in the case of wayward apprentices.
Certain trees have sap that is filled with magical potential. Their sap is harvested and distilled down to produce various types of potions, much like maple syrup is collected in some areas. The magical effects of these syrupy potions are often fairly trivial; perhaps they simply cause the imbiber to grow hair more quickly, summon butterflies, or walk a few inches above the floor. People enjoy the syrup as a flavoring, instead of imbibing it for its magical powers.