Uropygus

inhaled (toxin) - 600 gp
ToxinThe yellowish gas extracted from this poison greatly disturbs the coordination and the auditory system, which affects the balance.
A creature subjected to this poison must succeed on a DC 18 Constitution saving throw or fall prone. If the first saving throw is unsuccessful, the creature must repeat it at the beginning of each turn for 8 rounds. At each new failure, the creature falls prone again.
Recueil des poisons d´AideDD
  1. DnD 5e Poisons › Uropygus