GURPSよろず

p.76

　Truly diminutive combatants – for instance, those with high levels of Shrinking – should realistically enjoy certain benefits, despite their size.

　A tiny fighter is hard to see. Enemies attack him at a penalty equal to his SM. At SM -10 or smaller, when he attacks, his target must make a Vision roll. Modifiers include the attacker’s SM and the +10 to spot something in plain sight (see Vision, p. B358); e.g., SM -14 requires a Vision-4 roll. Failure means the defender doesn’t see the attack coming and gets no defense, as if his attacker were invisible.

　The natural weapons, Innate Attacks, and so on of a minuscule warrior scale in proportion to his body – as do weapons reduced by Shrinking. Being narrow, they can more easily target openings in armor.
If using Targeting Chinks in Armor (p. B400), reduce the penalty to hit by SM, to a minimum of 0. Those with SM -10 or smaller can target gaps in armor at no penalty. Of course, if you’re 1.8” tall, attacking anything but a foot is impossible without Flight or cunning tactics . . .

　By making a successful grapple, a fighter with SM -13 or smaller can crawl inside unsealed armor, where he can ignore its DR. If he can reach a nostril, ear, or other orifice, a successful grapple lets him get inside his foe’s body, where he can also ignore natural DR. No defense is possible against attacks from either vantage.

　At SM -19 and below, it’s possible to get into the bloodstream if injected or able to reach an open wound. Use the rules above, except that all attacks are effectively to the vitals (\3 wounding modifier). To enter the body through its pores requires SM -44 or smaller.

　All of this assumes an SM 0 opponent. In battles between tiny combatants, the difference in SM is what matters. For instance, if an SM -15 super is fighting an SM -10 foe, he applies these rules as if he had SM -5 and his enemy had SM 0.