The spirit cape does not work with a stat boost from a special move scroll, such as the wolpertinger. The spirit cape works with the unicorn stallion familiar, even though it is not a combat familiar, but not with the ghast familiar, despite similarities between its special and the unicorns. The cape only lowers the special attack cost of combat related attacks (with the exception of the unicorn). This means that, even with combat familiars such as the elemental titans, the spirit cape will not reduce the cool down of titan's constitution, since it is not a combat scroll.
When using the spirit cape players get an in-game message "Your spirit cape reduces the cost of your familiar's scroll." if it is not filtered.