Sorcery, Building Powers, and Rolls

[Kromm]

Originally Posted by philosophyguy

1. When does a roll lower the cost of a power?

When neither the underlying advantage nor modifiers other than Active Defense, Requires (Attribute) Roll, Requires (Skill) Roll, or Unreliable require such a roll. Many advantages require a roll; Mind Control is one example (a Quick Contest of IQ vs. Will is built in), and Healing and Warp are two others (IQ rolls are built in). Some modifiers other than those named above require rolls, too; notably, anything with Malediction picks up a Quick Contest of Will vs. either Will or HT, depending on the underlying advantage. The limitations Active Defense, Requires (Attribute) Roll, Requires (Skill) Roll, and Unreliable exist mainly for the purpose of adding rolls to abilities that don't require them for one of those other reasons.

Originally Posted by philosophyguy

2. What requires an Innate Attack roll?

Any offensive ability that doesn't require a resistance roll and isn't an Aura, Emanation, or other essentially passive effect. Notably, any Affliction, Binding, or Innate Attack not modified with Malediction, and any advantage modified with Ranged or Weaponized. Maledictions and anything that works like them (Mind Control, Neutralize, Possession, etc.) use resistance rolls, not Innate Attack rolls.

All of this is explained in detail in GURPS Powers. Sorcery hides that behind the curtain and directs the reader interested in creating new spells to that work.