Here is another spell from GURPS Magic I've chosen to modify for my DF game.
Phantom is basically Perfect Illusion with the ability to cause damage/impede movement. It's mostly okay, but:
- a Phantom can have ST and DX up to the mage's skill with the spell. That's probably okay in a game where skill 15 in a VH spell is uncommon, it's not when skill 19-20 in a VH spell is typical. DX 19 is pretty high. ST 19, well, that's okay.
- the "note the margin of success" for HP.
- An odd 5 to cast, 9 for double ST and DX (uh, yeah, because I want to allow DX 38-40?)
- it's not clear how the Phantom does its thing when cast without the Initiative spell. Which, by the way, contradicts Phantom on DX by assigning it an 8!
Here is the change:
As written, except:
- the Phantom has ST equal to the caster's skill in the spell for purposes of attacks and damage.
- the Phantom has DX 15.
- the Phantom has 4 HP.
- a victim can actively attempt to disbelieve - success means the victim treats it from then on a Perfect Illusion. Injuries and effects inflicted previously remain.
- the caster must concentrate to have the Phantom take any active measures, such as attacking.
Base Cost: 4. For a base cost of 8, the phantom has double the normal ST and HP.
That makes it slightly cheaper (4/8, not 5/9), easier to fend off, more consistent in its effects, and yet it is still valuable and dangerous.