Hit Die: d4.
Requirements
To qualify to become a master counterspeller, a character must fulfill all the following criteria.
Skills: Spellcraft 8 ranks, Knowledge (arcana) 8 ranks.
Feats: Improved initiative, Improved counterspell, Reactive counterspell
Spells: Able to cast Dispel Magic or Dispel Magic, Greater.
Special: The candidate cannot have any prohibited spell school(s).

Class Skills
The master counterspeller's class skills (and the key ability for each skill) are Bluff (Cha), Concentration (Con), Craft (Int), Decipher Script (Int), Diplomacy (Cha), Gather Information (Cha), Knowledge: Arcana (Int), Knowledge: Dungeoneering (Int), Knowledge: Nature (Int), Knowledge: Religion (Int), Knowledge: The planes (Int), Listen (Wis), Profession (Wis), Sense Motive (Ws), Spellcraft (Int), and Spot (Wis)
Skill Points at Each Level: 2 + Int modifier.

Level	Base Attack Bonus	Fort Save	Ref Save	Will Save	Special	Spells per Day
1st	+0	+0	+0	+2	Counterwave I, Keen eye for spells	+1 level of existing class
2nd	+1	+0	+0	+3	Counterwave II, Shortcut, Uncanny Counterspell	+1 level of existing class
3rd	+1	+1	+1	+3	Counterwave III, Opposite Effects	+1 level of existing class
4th	+2	+1	+1	+4	Counterwave IV, Experienced Counterspell	+1 level of existing class
5th	+2	+1	+1	+4	Counterwave V, Intuitive Reactive counterspell	+1 level of existing class
6th	+3	+2	+2	+5	Counterwave VI, Greater Counterspell	+1 level of existing class
7th	+3	+2	+2	+5	Counterwave VII, Opposite Targets	+1 level of existing class
8th	+4	+2	+2	+6	Counterwave VIII, Improved Uncanny Counterspell	+1 level of existing class
9th	+4	+3	+3	+6	Counterwave IX, Backfiring spell	+1 level of existing class
10th	+5	+3	+3	+7	Master Counterspell, Effortless Counterspell	+1 level of existing class

Class Features
All of the following are Class Features of the master counterspeller prestige class.
Weapon and Armor Proficiency: Master counterspeller gains no proficiency with any weapon or armor but they gain the proficiency to use shield.
Spells per Day/Spells Known: When a new master counterspeller level is gained, the character gains new spells per day (and spells known, if applicable) as if she had also gained a level in a spellcasting class she belonged to before she added the prestige class. She does not, however, gain any other benefit a character of that class would have gained. This essentially means that she adds the level of master counterspeller to the level of some other spellcasting class the character has, then determines spells per day, spells known, and caster level accordingly.

Counterwave: The Master Counterspeller gains one use of this ability per day for each spell level noted. This extra raw magical power acts as a spell that can be only used to counter same or lower level spell and it is treated as it would be excat opposite spell than the spell it counters for countering otherspells.
Altrough the Counterwave always produces a opposite effect than the target spell, regaldes if it normaly has a counter part, the Master Counterspeller can't anyway benefit from it or use any other of his abilites to change the countered spell.

Keen eye for spells: The Master Counterspeller may Take 10 when identifying spells using Spellcraft, even in stressful situations. Additionally, he gains a competence bonus equal to his Master Counterspeller level(s) to identify spells in this manner.
At 4th level, he auto-recognizes any spell he has currently prepared (or as Spells Known).

Shortcut: Counterspeller's usualy rapidly grow tired and frustrated to the spell components (or lack of them) as they can prevent their success in counterspelling, thus the master counterspeller works around this problem by practicing casting spells without the components. At this point he has mastered this feat thus he gains the feat Eschew Materials for free.

Uncanny Counterspell: The Master Counterspeller is never considered "flatfooted" when attacked by a spell, even if surprised or attacked by an invisible opponent. (In game mechanics, he keeps his DEX and dodge bonuses to AC against suprise/invisible/first-round RTA spells.)

Opposite Effects: If the master counterspeller successfully counterspells a spell and that spell has a spell that works as a counterspell, the spells effect is instead changed to that counterspells effect instead without counterspelling the spell. A Master Counterspeller may do this for a number of times per day equal to 3 + his Intelligence modifier.
Note that the targets remain the same and control over the spell stays with the caster whos spell was this way changed.
E.g. If the opponents castets Haste on his allies, master counterspeller could try to change its effect to Slow.

Experienced Counterspell: The Master Counterspeller gains a competence bonus to his counterspell level checks equal to his Master Counterspeller level(s). This point on, he can also use Reactive counterspell feat even if flatfooted.
E.g. 7th lvl Master Counterspeller would gain +7 competence bonus to his caster level check when resolving the result of using Dispel Magic for counterspell.

Intuitive Reactive counterspell: The Master Counterspeller can use the Reactive counterspell feat without loosing your next action. This ability can be used once per round and for a number of times per day equal to 3 + his Dexiterity modifier bonus.

Greater Counterspell: When counterspelling, you may use a spell of the same school that is the same spell level than the target spell. Also if the character posses the Heighten feat, he can use the feat when counterspelling without increased casting time.

Opposite Targets: If the Master Counterspeller successfully counterspells a spell, he can instead of countering its effect, change its targets opposite to the what the spells caster was targeting. A Master Counterspeller may do this for a number of times per day equal to 3 + his Wisdom modifier bonus.
E.g. Bless can be altered to affect master counterspeller's allies instead of opponents allies.

Improved Uncanny Counterspell (Ex): A Master Counterspeller of 8th level or higher can no longer be flanked by spells or spell-like abilities.
This defense denies rogue the ability to sneak attack the character with spells or spell-like abilities by flanking her, unless the attacker has at least four more caster levels than the target does.

Backfiring Spell: If the Master Counterspeller successfully counterspells a spell and so wishes, the spell is turned back upon the caster as if it were fully affected by a spell turning spell. If the spell cannot be affected by spell turning, then it is merely counterspelled. A Master Counterspeller may do this for a number of times per day equal to 3 + his Charisma modifier bonus.
Note: Per DnD 3,5 rules, only a spell that targets a creature can be turned, area spell(s) can not be turned.

Master Counterspell: When counterspelling, you may use any spell that is one or more spell levels higher than the target spell.

Effortless Counterspell: The Master Counterspeller has found a way to counterspells using flaws the spell itself contains thus he does not need almost any effort to counter them but as this needs great focus and a certain mind set he can do it for only limited number of spells. For each 5 levels of Master Counterspeller, he can chooce one spell that is counterspelled automaticly wihtout using any Master Counterspellers spells or resources but is as restricted as normal counterspelling is (thus he has to regognice the spell and be able to counter it). He can change one spell per each day that he can Effortleysly Counterspell. As this counterspell is made by ruining the spell foundation (like changing skyscraper foundation from stone to mud) the spells effect can not be exploited by other Master Counterspells abilites or any otherway. The spell is treated as the caster failed to cast the spell.

Ex-Master Counterspellers A Master CounterSpeller who looses access to all schools of magic, looses also all his class abilites.

From SRD: Magic Overview: COUNTERSPELLS
It is possible to cast any spell as a counterspell. By doing so, you are using the spell’s energy to disrupt the casting of the same spell by another character. Counterspelling works even if one spell is divine and the other arcane.
How Counterspells Work: To use a counterspell, you must select an opponent as the target of the counterspell. You do this by choosing the ready action. In doing so, you elect to wait to complete your action until your opponent tries to cast a spell. (You may still move your speed, since ready is a standard action.)
If the target of your counterspell tries to cast a spell, make a Spellcraft check (DC 15 + the spell’s level). This check is a free action. If the check succeeds, you correctly identify the opponent’s spell and can attempt to counter it. If the check fails, you can’t do either of these things. To complete the action, you must then cast the correct spell. As a general rule, a spell can only counter itself. If you are able to cast the same spell and you have it prepared (if you prepare spells), you cast it, altering it slightly to create a counterspell effect. If the target is within range, both spells automatically negate each other with no other results. Counterspelling Metamagic Spells: Metamagic feats are not taken into account when determining whether a spell can be countered
Specific Exceptions: Some spells specifically counter each other, especially when they have diametrically opposed effects.
Dispel Magic as a Counterspell: You can use dispel magic to counterspell another spellcaster, and you don’t need to identify the spell he or she is casting. However, dispel magic doesn’t always work as a counterspell (see the spell description).

From SRD: SpellsD-E: Dispel Magic
Counterspell: When dispel magic is used in this way, the spell targets a spellcaster and is cast as a counterspell. Unlike a true counterspell, however, dispel magic may not work; you must make a dispel check to counter the other spellcaster’s spell. You make a dispel check (1d20 + your caster level, maximum +10) against the spell or against each ongoing spell currently in effect on the object or creature. The DC for this dispel check is 11 + the spell’s caster level. If you succeed on a particular check, that spell is dispelled; if you fail, that spell remains in effect.