I'd like to share my thoughts on this topic.
My intent here is to make Certamen a real combat method as well as a dueling method. I have also made Parma stronger in order to make the Certamen tactically favourable in more circumstances.
Anyway tell me what you think.
Revised Parma and Certamen
Parma creates a magical ward about the caster or a group which includes the caster. The Parma Magica ritual has a casting time of one diameter and duration of Sun.
A Parma Magica ward provides a base magic resistance of Parma skill level x 5. In addition, the Parma caster's Form score that corresponds to the incoming effect is added to the Magic Resistance. These Form bonuses do not provide Magic Resistance independent of Parma. Without Parma the magus has no magic resistance.
If the magus considers himself in immediate danger of magical attack he can go 'on guard'. In this state the Parma Magica surrounding the magus (or group) becomes visible as a faint cloud extending about a foot from his body. The cloud swirls with colors corresponding the Forms and Techniques. This cloud generates no light itself; therefore its visibility depends on local lighting. Maintaining the 'on guard' state requires a fatigue test every minute.
While 'on guard' the magus automatically adds his Technique score that corresponds to the incoming effect, to his Magic Resistance.
The magus can also make his Magic Resistance particularly affective against one Form. He can spend a Fatigue Level to double one Form bonus. This extra protection lasts for a diameter, but only one Form enhancement can be active at any one time. He may also expend a Fatigue Level to prevent his Parma collapsing via a Certamen attack; doing so restores is to full function.
The Certamen ritual is method of casting a spell that first acts to dispel any Parma Magica the Target may have. All Hermetic magi can employ this casting method.
The Certamen attacker first decides on a spell. The spell must affect the Target directly, rather than through a medium, but otherwise any spell may be cast via a Certamen ritual. The caster must first successfully cast the spell, fulfilling all necessary conditions of the spell, such as range, line of sight or arcane connection. If the spell is successfully cast a Certamen phantasm forms and the Certamen combat begins the following round. The phantom takes on a form appropriate to the spell it embodies.
Casting a spell via a Certamen ritual creates an obvious visible affect, as the Certamen phantom forms before the caster. This gives alert opponents the option of generating their own phantom the same round; this allows for simultaneous engagement the following round. Alternatively the magus can trust their raw Penetration and simply cast a spell normally. Spells like Wind of Mundane Silence may also be used to dispel the phantom directly.
If the Target (or magi within the Target) has no active Parma Magica the spell proceeds as normal. If the Target does have an active Parma a Certamen combat proceeds.
A Certamen combat may be one-sided. In a one-sided combat the defender does not have a Certamen phantom to contest the field. A one-sided Certamen attack consists of a phantom battering down the defenderâ€™s Parma Magica uncontested.
The defending magus may fight back however he chooses, using either normal casting or Certamen phantom; he may even attack physically if he chooses. However, he cannot escape a Certamen phantom by moving out of the spellâ€™s range or line of sight. Once it has begun the Certamen ritual maintains the link.
If the defender(s) decides to counter-attack via a Certamen phantom, he needs to spend a round conjuring the phantom; as the attacker did. The phantom then engages its opponent the following round. Unless the defender started conjuring his phantom in the same round as his opponent, the first Certamen round is one-sided.
When both are conjured the phantasms battle to and fro between opponents. In the case of Arcane Connection Ranges, a window of sorts appears before each combatant through which the phantoms battle. If he is being attacked at Arcane Range he may attack back with an Arcane Range spell. The active Certamen ritual provides the defender with a useable Arcane Connection for such counter-attacks.
Each round the Certamen attacker and counter-attacker(s) generate a Penetration total for their spells (the phantoms); this is the strength of their Certamen phantom. The strengths of the opposing phantoms are compared and the difference determined. This difference is subtracted from the Magic Resistance of the magus with the weaker phantom, representing the damage done to their Parma Magica. If a magusâ€™s Magic Resistance ends the round at zero the opponentâ€™s spell takes effect. Additionally the Parma Magica ritual is completely dispelled and needs to be re-cast. At this point the magus has no Magic Resistance.
Unless a defending magus is incapacitated or unconscious he is automatically considered â€˜on guardâ€™. At any time he may also choose to expend a Fatigue Level in order restore any damage done to his Parma Magica by Certamen attacks. The restoration can occur after all phantom attacks have been resolved; thus he can avoid complete Parma failure (note that a magus may find himself facing multiple phantoms).
A Certamen attack continues until one of the following occurs: the phantom is dispelled, the spell takes effect, the caster is unable or unwilling to continue, a failed concentration check or a botched a roll. If this happens the corresponding phantasm disappears and the Certamen combat becomes one-sided or ends. If they are still able, the magus can re-join the Certamen field by conjuring a new phantom. A magus may decide to abandon a phantom in order to change their spell. Whether they lose a phantom willingly or not they are left undefended for at least a round.
If the Target contains multiple magi with active Parma Magica, the Certamen attacks are run in parallel. The spell only takes effect if all Parma based Magic Resistances are reduced to zero.
Normally, in a formal Certamen dual, the first magus to land a spell successfully wins. However, the dual may continue for any number of spells until one party concedes or cannot continue.