An admittedly unusual situation came up, and I'm interested to see if I interpreted it right.
Cthulhu vs Hastur, Cthulhu plays out Feathered Serpent and Yig.
Cthulhu commits the Feathered Serpent to a story. Action window opens up, Cthulhu changes one of the [Terror] icons on the Feathered Serpent to a [Combat][Arcane], as per its ability. Hastur responds with Socotophobia.
What icons does the Feathered Serpent have?
Here's how I read it. Unfortunately, FAQ 1.11 doesn't work really well, as in this case, you can't just add up the icons, due to the "printed [Terror]" qualifier on Socotophobia. So, first of all, one of [Terror] icons was already changed to [Combat][Arcane], so it keeps both of those. Socotophobia removes all "printed" [Terror] icons - but that's only two icons left. Yig adds one [Terror] icon, so that one remains. Final icon count, [Terror][Combat][Arcane].
Alternately, you could read Socotophobia "printed [Terror]" as meaning "as many [Terror] icons as are printed on the card". In that case, it's a simple matter of math: Serpent has three (three printed, minus one transformed, plus one Yig), and then loses three due to Socotophobia, final total zero. I don't favor that interpretation, however, as it's less intuitive. The way Socotophobia is written, it sounds like you start with the character as printed, zero out all its printed Terror icons, then calculate what's left from there.
Which is correct?