So, I'm pretty new to being an arcane caster. Let's just make that clear. Anyway, I'm playing with a caster level 7 pale master wizard and I come across my first beholder (VON 2) as an arcane. Although I didn't know what particular spells worked well against them, I thought I heard that Phantasmal Killer was effective. So I made certain to have that spell ready. My wizard is an elf and I do have the first two tiers (I think I got two, not just one) of the Elven Arcanum enhancements. I don't recall if I had any other equipment or items on that increased my spell pen or DC. So, when I went to cast the PK spell a couple times, the beholder saved the spell each time thus causing nothing to happen.
This is the part that always confuses me and I just can't seem to get my head around it. In this particular example, what would be needed to make the PK spell more effective? Increasing spell pen or DC? I find it really difficult to grasp the two.
Explain to me how these two work and how they are effective.
Thanks for your help.