You attempt to interrupt a creature in the process of casting a spell.
The target spell must have a casting time of or greater. spells, and spells, cannot be counterspelled, they are too fast to counter.
Both casters make a contesting roll. They both roll + Bending Skill.
Then the additional modifier is added to the counterspeller's roll: [spell_level_cast] - 3 (level of counterspell). Meaning, higher level spells are more difficult to counterspell.
A final modifier is added to the counterspeller's roll: if the counterspeller knows the spell, or is able to cast the spell, the counterspeller adds +2 to their roll.
This check is determined by the GM (or Janus automatically):
Anticipating your foe's incantation, you twist your hand into a tight fist, crushing the image of extinguishing a candle's flame. These synchronized motions unleash a prepped magical construct, snuffing out your opponent's spell with a swift, unseen force.
I Cast Counterspell
I observe the spellcaster, akin to a bird monitoring an ant. Just before the penultimate syllable, I act, inducing a familiar numbness in my hand. With a precise cutting motion, I sever their connection to summoned energies, nullifying their spell with a touch of mastery.