pf2e.fyi
From Pathfinder Impossible Magic, which isn't enabled.

Serpent's Lash

ITEM 8
UNCOMMONDISARMFINESSENONLETHALREACHTRIP
Price 450 gp
Usage held in 1 hand
Bulk 1
Category martial
Group flail
Damage 1d4 slashing

This +1 striking whip was fashioned with the enchanted leather of a giant serpent. Several vicious fangs are embedded in the thong and fall of the whip. When wielded in combat, the weapon emanates a faint rattling sound.

Activate—Slither Strike
Frequency once per day
Trigger A creature within reach Casts a Spell with the manipulate trait
Effect You Strike the triggering creature with the whip. If you hit and deal damage, you also Reposition the creature 5 feet (10 feet on a critical hit).
Pathfinder Impossible MagicORC