I finally got Billy during the Fate/Zero event and as he's my favourite Archer, I want to get the most out of him as possible. I planned to place Knight's Dignity on him but his Evade no longer applies Defense up on him anymore, so I'm kind of at a loss. Currently have Gem Magecraft: Antumbra on him.
I run billy with mlb imaginary around as a last line of defense and usually don't play him as a crit archer even though his crit buff is broken. Dignity is too risky, Antumbra is fine. My recommendation would be to go Holy Night Sign on him because different types of buffs work using multiplication so it would be the best damage wise for billy. Volumen Hydrargyrum came out so it would be the best defensive option for him.
You have plenty of choice.
If you want him to be able to deal more damage overall, go for Art of Death, Imaginary Around, Gandr or any other quick CE
If you want him to do crit damage, Antumbra, Knight's Dignity (if you can keep him alive, I personally run him with the likes of Mashu or Andersen with this), Holy Night Sign
You can also give him star absorb CEs like Teacher and I or Self Designated Enforcer so he can run along with high star absorbs quick supports like Alexander or Atalanta
The best CE for him imo is Golden Sumo, it gives him 15% attack AND 50% NP charge at MLB, he can immediately fire his NP when his 2nd skill is maxed, and perma 15% attack is basically only 5% lower than waver's 3rd skill maxed. Though it isn't available yet right now, it will be available later in the event shop of the Onigashima event.
