Riddle in Thirteen Lines!

Question

It loves to twist and turn,
A mystery that men seek to learn.
I don't doubt its swag,
It can make an ant nag.
It takes one so far,
And builds a nice bar.
It's powers can be seen,
When it transforms a barren terra green.
Never does it fail,
When it makes one envy for rail.
It's cryptic, not so complex,
A weak clerk is now a strong Pyrex.
It asks you, "What am I?"

Answer 1

The answer is:

the cipher rot-13 (i.e. a Caesar shift of 13 letters, so that A becomes N, B becomes O, C becomes P, etc.) commonly used here on Puzzling to hide information in comments.

This is hinted at by the use of thirteen lines in the riddle itself (and the title).

It loves to twist and turn,
A mystery that men seek to learn.

rot-13 is a cipher, i.e. a way to disguise or twist your writing, to make your words mysterious.

I don't doubt its swag,
It can make an ant nag.

ANT becomes NAG (and vice versa) in rot-13.

It takes one so far,
And builds a nice bar.

ONE becomes BAR (and vice versa) in rot-13.

It's powers can be seen,
When it transforms a barren terra green.

TERRA becomes GREEN (and vice versa) in rot-13.

Never does it fail,
When it makes one envy for rail.

ENVY becomes RAIL (and vice versa) in rot-13.

It's cryptic, not so complex,

It may appear mysterious but is still a relatively straightforward cipher to decrypt.

A weak clerk is now a strong Pyrex.

CLERK becomes PYREX (and vice versa) in rot-13.

It asks you "What am I?"

Well, or does it in fact ask...

"Jung nz V?"!