It seems that you're using an outdated browser. Some things may not work as they should (or don't work at all).
We suggest you upgrade newer and better browser like: Chrome, Firefox, Internet Explorer or Opera

×
The skull spells seems good to be amplified. The sheild spell is also nice. My Ectoplasm is at full.
In my own playthrough, I had the same idea. I went for shield first of all, then skulls.