What are the best magical systems in GURPS?

[AlexanderHowl]

Immunity works against effects of that type that do not allow for Resistance rolls (for example, Cyanide for Poisons and Malaria for Disease), so Immunity (Magic) works against all magical effects that target a character, whether they are resisted or not (unless DR or Protect Sense provides protection). There are diseases and poisons that potentially have beneficial symptoms (for example, a Fatigue Attack with Contact Agent could give Regeneration), but Immunity (Disease) or Immunity (Poison) would also prevent them from working.

[kirbwarrior]

Originally Posted by AlexanderHowl

Immunity works against effects of that type that do not allow for Resistance rolls (for example, Cyanide for Poisons and Malaria for Disease), so Immunity (Magic) works against all magical effects that target a character, whether they are resisted or not (unless DR or Protect Sense provides protection). There are diseases and poisons that potentially have beneficial symptoms (for example, a Fatigue Attack with Contact Agent could give Regeneration), but Immunity (Disease) or Immunity (Poison) would also prevent them from working.

It only works against very specific effects that don't allow Resistance rolls and even tells you them in Basic. Further;

Originally Posted by Kromm

ItMH means that no chemical, disease, or similar agent that alters your metabolism to cause the afflictions on pp. B428-429, or indirect FP or HP loss, affects you. This includes ones that word their afflictions as temporary disadvantages.

Originally Posted by Kromm

Noxious effects only, defined as being ones that cause afflictions (pp. B428-429 and temporary disadvantages), FP loss, and/or HP loss. If some miracle drug cures cancer, grants 10 bonus HP, and gives you Mind Reading, but also lowers your ST to 1 and causes Paranoia, you simply don't suffer the ST loss or Paranoia.

Noxious Effects only. If a "poison" gave High Pain Threshold and did 3d fat damage, you'd ignore the damage. And if we assume the rules work the same for any power as it does the "mundane" powerset, Immunity to Metabolic Hazards is still better than Immunity to Magic (or psionics, super, etc). If a character was untouchable by Magic, that character should get the far superior defenses Static gives with the downsides of not being able to be buffed, healed, etc by Magic. (It's also pretty antagonistic to have an advantage on your sheet "protect" you from beneficial effects when that isn't written out plainly).

On topic, I also like "Magic as TL" where the 'tech' of the setting is actually just magic being commonplace. "Magic as Bang!" is a pretty fun subtle system where you pick a wildcard skill and treat the effects as magic, including things like impulse points the bang skill gives.