Troll Vomit

A Troll's digestive fluid is the most corrosive thing known to science... and about the most revolting too. Trolls are able to vomit their stomach contents upon their enemies if they wish.
A unit of Trolls can make Vomit Attacks instead of ordinary attacks during close combat. Each Troll can make only 1 Vomit Attack at a time as opposed to 3 ordinary Attacks. Vomit Attacks always hit and always penetrate armor due to the corrosive semi-liquid nature of Troll Vomit. Therefore, a Vomit Attack automatically hits and inflicts a single S5 hit with no armor save allowed.