Arrow of the Viper

1d10 green-tinged arrows have a fanged snake head at the point and fletching reminiscent of bat wings.
When loosed it seeks any target within 300 feet (even behind total cover), moving like a tiny winged serpent.
An attack roll is still required, but if successful it deals normal damage and the target must make a DC 16 Con save or be poisoned for 1 hour.