(Lee Barklam - with contributions from Kharille from the DragWars Yahoo Group)
There are a couple of spells that explicitly state that they cause deafness, the Banshee spell and the Darkness version of Garrotte, but do not explain the impact of deafness on the game mechanics.
The Mystic's Thunderclap spell does not explicitly state that it causes deafness, but it seems reasonable to assume that it would be a side-effect of anyone struck by the force of the spell that is not instantly killed by it. Other loud\explosive spells may cause a temporary ringing in the ears that may result in a tempoarary penalty, but I think that opens the door to a lot of number crunching for other temporary side-effects of spells (such as temporary blindness, nausea, deafness, etc.) that runs counter to the simple spirit of the Dragon Warriors system.
So, assuming a character has been struck deaf by a dragon's roar, a magical spell, curse, or Sufuriad's wail, this article proposes a number of effects on perception, stealth, combat and spellcasting, with a special mention of demonology. This article is a collaborative work in progress and contributors' names (where known) have been included at the top of this article.
Deafness should only play a part in perception when there is an auditory element to the check, not visual - purely visual perception checks would be unaffected. Where there is an element of both the visual and the auditory, such as detecting someone sneaking, potentially scuffing a shoe or breaking a twig, then maybe a -2 to -4 penalty would be applicable, depending on how important the GM considers the auditory element would be.
Deafness certainly would improve the effectiveness of invisibility, providing infallible stealth against a deaf character.
Not being able to hear whether whether you are making a noise yourself, when attempting to move silently or hide, for example, should incur a -4 penalty to Stealth. Where the Stealth attempt is for a visual-only deception (disguise attempt, perhaps), being deaf should apply no penalty. Where there is a primarily visual, but also an important auditory element, to a Stealth attempt (such as impersonating an accent as part of that disguise), a -2 penalty to Stealth applies.
Being unable to hear could impact combat effectiveness, but not as much as being blind. A -2 penalty to both Attack and Defence scores when in melee combat seems reasonable, with no penalty for ranged combat. Surprise, however, should occur on a roll of 1-3 on a d6.
Spells that require an element of verbal incantation to cast (i.e., all but Mystic spells) could potentially be miscast. Experienced magickers would be more familiar with the incantations and be less likely to miscast a spell but more powerful spells (presumably with more complex incantations) would be more likely to be miscast. A spell miscast suffers the same consequence for the magicker as detailed for spell failure on page 77 of the main rulebook. The following suggested formula could be used to determine if a spell is miscast:
If the sum of 1d4 and the spell level is greater than the magicker's rank, the spell has been miscast.
Note that this formula means that magickers will NEVER be able to cast a spell of a level equal to their rank and only have a 25% chance to cast spells from the previous level. Some players may feel crippled by this limitation and the GM should be encouraged to work with their players to discuss a more appropriate game mechanic.
Unlike normal spellcasting, the lengthy rituals performed by Demonologists would be particularly prone to mispronunciation and failure than spells that can be incanted in a single round.
The Ritual of Summoning suffers a -6 penalty to the Demonologist's Magical Attack, reduced by 1 for every rank of the Demonologist above 5, to a minimum of -1.
Banishing a Demon is made with a -4 penalty to the Demonologist's Magical Defence, reduced by 1 for every rank of the Demonologist above 5, to a minimum of -1.Calling a demon bound with the Pact of the Dark Companion has only a 10+rank% chance of working each round (maximum 20% chance at 10th rank).The chance of miscasting a Posession spell is equal to the normal spellcasting failure chance (see above), but the die rolled is a d6 to represent the additional length and complexity of the incantations.The Curse of Asterion is unaffected by deafness.
Lastly, of course, deafness is not an all or nothing thing - there are degrees of deafness such that you might want to roll 1d6 (or d4, d8, etc.) the first time someone is exposed to a cause of deafness to determine the severity of the deafness. Every time the same character is exposed to another cause of deafness, the severity increases by 1 until it reaches 6 (or 4 or 8, etc.), at which point the character is considered totally deaf. Pro-rata penalties for partial deafness should still be applied.
Introducing permanent disabilities (permanent loss of a limb, loss of a primary sense), etc., may not be in keeping with many players' expectations of the game and the role-playing implications of playing a deaf character should be considered before being introducing it.
Consider also the challenge of ignoring conversations overheard at the gaming table and discounting that player knowledge when directing your character - such play can be frustrating, even more so than playing a blind character.
Deafness (and blindness and the loss of limbs) is most suitable for NPCs to provide more 'flavour' to the character. Unless the NPC is unusually provocative or the players are unusually aggressive, the GM is unlikely ever to need rules to govern how a deaf character is impaired in combat or spellcasting and is free to apply on the spot penalties as he sees fit.