Well, in RE2, William just flees after you shoot a few Magnums (usually aroudn 10 to 20) into him. I would assume he flees because he senses danger, or is threatened...

It is true that he can march through the bullets... in fact he did in the early forms, but he marches through them slowly and sustains damage. If a mere human such as Leon and Claire can outrun (outwalk?) and shoot him, then...

Dante's attack is not purely elemental. Yes, he creates Fire and Wind when he spins the Agni & Rudra (And they have power granted by the Demon Twins gate keeper!), but the swords themselves would actually cut as well. As for the effectiveness of Fire? Even the Flame Rounds can hurt William.

I would say that Electricity will hurt William. The power of Spark Shot can hardly compare to that of Nevan (Nevan is actually a demon, and the weapon has the power of that demon). The bat doesn't bite, they charge into their foes like bullets. Electrically charged homing bullets.

Also, Tune up isn't magic... I see it asa Sonic Wave more than anything.

As for Thunder Bolt and Vortex, I forgot to mention that Dante is invulnerable during Vortex.