Enchanted arrows. A pixie bow (which only works when used by a pixie) automatically enchants arrows it fires. An arrow which damages a target renders it Drowsy, Distracted, or Tipsy  as chosen by the pixie.
Truesight. Pixies can clearly see invisible creatures, through illusions and disguises, and see clearly in the dark.
Invisibility (1). Pixies can become invisible at-will by simply spending an action. Becoming visible again does not require an action.
Cantrips (1). Pixies can cause any minor effect with the power level of a cantrip. This only costs them one action.