Discipliner
This is less of a path than it is a separate Discipline, as the power to resist Thaumaturgy can be taught independently of Thaumaturgy, even to those Kindred who are incapable of mastering even the simplest ritual. However, the techniques of Thaumaturgical Countermagic are not officially taught outside Clan Tremere, for obvious reasons. Any non-Tremere who displays the ability to resist Thaumaturgy quickly becomes the subject of potentially fatal scrutiny from the entirety of Clan Tremere.
System: Thaumaturgical Countermagic is treated as a separate Discipline. It cannot be taken as a character's primary path, and a rating in it does not allow the character to perform rituals. The use of Thaumaturgical Countermagic is treated as a free action in combat and does not require a split dice pool. To oppose a Thaumaturgy power or ritual, a character must have a Thaumaturgical Countermagic rating equal to or greater than the rating of that power or ritual (which means that rituals of Level Six or greater cannot ever be countered with this power). The player spends a blood point and rolls the number of dice indicated by the character's Thaumaturgical Countermagic rating (difficulty equal to the difficulty of the power in use). Each success cancels one of the opposing thaumaturge's successes.
Thaumaturgical Countermagic can only be used against Tremere Thaumaturgy at full effectiveness. It works with halved dice pools against non-Tremere blood magic and mortal "hedge wizardry," and is completely ineffective against non-vampiric magics and powers. Thaumaturgical Countermagic can be learned by characters who are unable to learn Thaumaturgy (e.g. those with the Merit Magic Resistance). Any non-Tremere character with a rating in this power automatically gains the Flaw Clan Enmity (Tremere), receiving no freebie points for it. This power cannot be taken during character creation and cannot be spontaneously developed. It costs the same as any other non-clan Discipline to learn.
For Example: Jaeger is a Tremere archon with Thaumaturgical Countermagic 5. He is facing Nadine, an infernalist with Lure of Flames 5. Nadine attempts to use her Lure of Flames to hurl a fireball at Jaeger and rolls two successes against a difficulty of 8. Jaeger rolls 10 dice of countermagic against a difficulty of 8, the same difficulty against which Nadine rolled, and scores three successes, completely neutralizing the attack.
Jaeger's partner Nathaniel has Thaumaturgical Countermagic 4. If Nadine had attacked Nathaniel, he would have been completely unable to counter the fireball, as his Thaumaturgical Countermagic rating is lower than that of the power being used against him. Likewise, if Nadine used her Movement of the Mind 4 to hurl a stake at Nathaniel, he would have been unable to oppose it because he cannot yet counter spells that target things that he is not touching.