An Ampoule "Knife" is shaped like an Incandescent light bulb. The grey handle is the screw cap of the light bulb. The "blade" has a yellow tint along the edges, and the silver filament is faintly visible at the base of the blade. The rest of the blade is white.
Its design is an obvious reference to Larxene's power over electricity, and possibly her "hot-headed" personality.
Ampoule is French for "Light Bulb".
These knives have the same combos as Vol de Nuit. Both the ground and aerial combos are identical to the Foudre combos, minus the -combo. The -combo consists of Larxene leaping into the air and performing a vertical spin. After this, you are prompted to press again, making Larxene perform her aerial finisher.