I have been playing my old CoC CCG game.

Several cards say something to the effect of "destroy all encounter characters" (Expl:. "A Time to Sow" ).

What are the blasted "encounter characters", are they the ones committed to a story, characters which say the word encounter on them, something else entirely?

Thanks in advance for answering this question.

"Encounter" characters are characters whose subtype is Encounter

Vampiricus said:

If you have a card that reads "Destroy all encounter characters" chances are you are holding one, since this text only appears on encounters. These are events that turn into a character with the Encounter subtype.

Ofcourse, you can 'cheat' a little using:

-- Miskatonic University --
M.U. Science Building
---------------------
Type : Support
Cost : 2
Subtype : Location.
Game Text: Action: pay 2 to choose a character or support card. Until the end of the phase, that card gains a Subtype of your choice.
Flavor text:
Illustrator: Mike Yamada
Collector's Info: AE U58

-- Yog-Sothoth --
Dream Messenger
---------------
Type : Event
Cost : 1
Subtype : Spell.
Game Text: Disrupt: before an Action or Response resolves, choose a character or support card in play. Until the end of the phase, that card gains a Subtype of your choice.
Flavor text:
Illustrator: Franz Vohwinkel
Collector's Info: AE R166