Blue
Ravenous Bugblatter Beast of Traal
Official stand (listed in the Sage Advice Compendium) is that the Subtle metamagic prevents Counterspelling because you can not tell a spell is being cast.
This is backed up by the Perceiving a Caster at Work section of Xanathar's Guide to Everything (pg 85).
So it would follow that a spell without Verbal components would not be eligible to be counterspells if the caster was Invisible or hidden during the casting for the same reason - the Counterspeller would not be able to perceive the spell being cast.
Which leads me to the question of recognizing Verbal components to determine if a spell is being cast. If the Counterspeller is in Silence they would not be able to detect the Verbal components even assuming they could cast (such as with Subtle). Same if the Counterspeller was Deafened.
Just as a creature may not be seen, and can hide in order to improve those chances, what is the equivalent for hearing Verbal components.
The PHB gives no guidance about how loud Verbal components are:
Now, all that is needed is to recognize a spell is being cast, which seems like a lower bar than making out the actual words or identifying the spell. But is always a given that Verbal components are heard, or could either environmental conditions (loud, windy, etc.) and/or a character attempting to hide the Verbal components (speaking softly, etc.) that could potentially cause the Counterspeller not to perceive the casting?
And the flip side - is it possible to use an action to mimic casting such that a Counterspeller perceives a spell is being cast. As per Xanathar's it is possible to cast a spell without a valid target - to no effect and the slot is lost. Such as using an action to mimic casting and if the Counterspeller is deceived and uses their reaction to cast a Counterspell, then casting a Bonus Action spell.
If a sorcerer casts a spell with only verbal or somatic components using Subtle Spell, can an opponent use counterspell against it? If a spell that’s altered by Subtle Spell has no material component, then it’s impossible for anyone to perceive the spell being cast. So, since you can’t see the casting, counterspell is of no use.
This is backed up by the Perceiving a Caster at Work section of Xanathar's Guide to Everything (pg 85).
So it would follow that a spell without Verbal components would not be eligible to be counterspells if the caster was Invisible or hidden during the casting for the same reason - the Counterspeller would not be able to perceive the spell being cast.
Which leads me to the question of recognizing Verbal components to determine if a spell is being cast. If the Counterspeller is in Silence they would not be able to detect the Verbal components even assuming they could cast (such as with Subtle). Same if the Counterspeller was Deafened.
Just as a creature may not be seen, and can hide in order to improve those chances, what is the equivalent for hearing Verbal components.
The PHB gives no guidance about how loud Verbal components are:
Most spells require the chanting of mystic words. The words themselves aren't the source of the spell's power; rather, the particular combination of sounds, with specific pitch and resonance, sets the threads of magic in motion. Thus, a character who is gagged or in an area of silence, such as one created by the silence spell, can't cast a spell with a verbal component.
Now, all that is needed is to recognize a spell is being cast, which seems like a lower bar than making out the actual words or identifying the spell. But is always a given that Verbal components are heard, or could either environmental conditions (loud, windy, etc.) and/or a character attempting to hide the Verbal components (speaking softly, etc.) that could potentially cause the Counterspeller not to perceive the casting?
And the flip side - is it possible to use an action to mimic casting such that a Counterspeller perceives a spell is being cast. As per Xanathar's it is possible to cast a spell without a valid target - to no effect and the slot is lost. Such as using an action to mimic casting and if the Counterspeller is deceived and uses their reaction to cast a Counterspell, then casting a Bonus Action spell.