HGd10PHB - Special Attacks - Counterspell

Counterspell is a Response Action that is specific to Actions involving Mystical Spells or Abilities. Counterspells come in two varieties.
=== Arcane Counterspell ===
Those who use the Arcane Spectrum may use Arcane + Transform to counter any spell or mystical ability targeting themselves or another target within line of sight and within Range of their spell casting ability. 
* To counter a spell in this way requires an Arcane+Transform roll 5 higher than the original spell's roll.
*The counterspell automatically consumes an amount of MYR equal to the MYR cost of the original spell.
**If the counterspell costs more than the caster has, it consumes all the remaining MYR and the counterspell does not work.
**If the original spell does not cost MYR, then the cost of the counterspell is 5 MYR.
**If the counterspell caster does not use MYR, then components are consumed regardless of outcome.
* If successful, the original spell simply dissipates into harmless arcane energy that has been used up and cannot be used for anything else. Such energy has no mass or velocity and is immediately absorbed by the arcane flow of the world. 
* Arcane Counterspells are Indirect by nature and immediately reach their target when cast without passing through the intervening space. 
* The only way to Counterspell an Arcane Counterspell is to roll a Mysticism check equal to or higher than the Counterspell caster's roll to determine that is what is being cast.
**If the Mysticism check is successful, an Arcane+Transform roll is rolled normally as per any other counterspell.
=== Spectrum Counterspell ===
The second kind of counterspell is a Spectrum-based counterspell. This kind of counterspell is context related. This means that the original spell is producing some effect and the counterspell is going to attempt to overcome that effect. There are two ways for a Spectrum counterspell to work.
# Same Spectrum+Transform - in this form, the counterspell caster will roll a Mysticism check equal to or greater than the original spell roll.
#* If successful, the caster knows what Spectrum is being cast and what the effect will be before it hit and may attempt to counterspell.
#* To counterspell, the caster needs to have the same Spectrum as the original spell available and the Transform Purpose. The caster rolls Spectrum+Transform and must roll 5 higher than the original spell and consume an equal amount of MYR as the original spell.
#** If the counterspell costs more than the caster has, it consumes all the remaining MYR and the counterspell does not work.
#**If the original spell does not cost MYR, then the cost of the counterspell is 5 MYR.
#**If the counterspell caster does not use MYR, then components are consumed regardless of outcome.
#* If successful on the counterspell roll, the caster may transform the spell into another, harmless form that represents that Spectrum.
#* If unsuccessful, the original spell activates as originally intended.
# Opposing Spectrum+Defend - in this form, the counterspell caster will roll a Mysticism check equal to or greater than the original spell roll.
#* If successful, the caster knows what Spectrum is being cast and what the effect will be before it hit and may attempt to counterspell.
#* To counterspell, the caster needs to have the opposing Spectrum to the original spell available and the Defend Purpose. The caster rolls Spectrum+Defend and must roll equal to or higher than the original spell and consume an equal amount of MYR as the original spell.
#** If the counterspell costs more than the caster has, it consumes all the remaining MYR and the counterspell does not work.
#**If the original spell does not cost MYR, then the cost of the counterspell is 5 MYR.
#**If the counterspell caster does not use MYR, then components are consumed regardless of outcome.
#* If successful on the counterspell roll, the caster may use their spectrum to defend against the original spell in a manner that represents the Defending Spectrum.
#* If unsuccessful, the original spell activates as originally intended.