Introducing 'Unknown Entities'

I have frequently disagreed with a Telic Thoughts commenter who goes by the moniker of The Pixie. However, he made a comment in an active thread which I believe is noteworthy:

"No, invoking a new, unknown entity is the antithesis of parsimony!"

The key phrase is "unknown entity." Ironically it has become a routine tactic of ID critics who generally invoke such unknown entities in response to ID concepts like irreducible complexity or ID critiques of origin of life theories. The unknown entities tend to take the form of imaginary biochemical pathways. Rather then provide specifics about the pathways themselves the focus is placed on phenomenon like random mutation and natural selection with logical argument filling in for empirical data.