> I am not the descendant,
> I beg your pardon please,
This clue is a wordplay with the with an antonym for scion — descendant. Descendant is also used to hide this literal clue by association with the Ascendant!
> And I refuse to be grafted
> on any old degree.
For each degree there is only one antiscion.
> If you can count backward,
> that’s the way you find me best.
An antiscion can be easily found by subtracting the position of the planet from 29 deg 60 and then looking for the mirror position in the Cancer/Capricorn axis (for example all antiscia of Cancer are found in Gemini). This is what is meant by “counting backwards”.
> And while you’re at it,
> you’ll know what I’m against.
If you have found the antiscion you also have the contra-antiscion which is opposite it.
Next riddle in a day or two!