Bloat

Bloat is a deadly poison known to be made by Assassins from the liver of the deep- sea blowfish. It makes its victim briefly impersonate a Zeppelin, swelling to perhaps two thousand times normal. Shortly afterwards someone has to do something about the 'splash', though; an outdoor venue is preferred.

Bloat is very very expensive, and few assassins are likely to use it anyway, since it obviously lacks class. It's another reason why Assassins' darts are engraved in Braille.