Qwilfish drinks over 2.6 gallons of water to inflate its spiky body, then uses the pressure to shoot poisonous quills, though it is briefly defenseless right after firing. Its Hisuian form, covered in dark purple-tipped spikes, can spray poison directly from its spines and is able to evolve into Overqwil, while the original Johtonian Qwilfish cannot evolve at all. Bulbapedia notes Qwilfish and its Hisuian line are the only Poison types with fins and the only Poison types in the Water 2 Egg Group.
Qwilfish made its animated debut in Dueling Heroes, where a trainer named Harrison used one against Misty's Corsola in the Whirl Cup. In Just Add Water, a Gym Leader named Dorian used a Qwilfish in an underwater battle to defeat Misty's Goldeen.
Qwilfish debuted in Neo Revelation as a Common illustrated by Sumiyoshi Kizuki. Astral Radiance later gave its Hisuian form two separate Common printings, and the Mega Evolution era added a Chaos Rising printing illustrated by nisimono.
Qwilfish's first card, a 2001 Neo Revelation Common illustrated by Sumiyoshi Kizuki.
A Hisuian Qwilfish Common from Astral Radiance illustrated by Kagemaru Himeno.
A Chaos Rising printing illustrated by nisimono.
The original Johtonian Qwilfish cannot evolve, but the Hisuian form can evolve into Overqwil.
A trainer named Harrison battled Misty's Corsola with a Qwilfish in Dueling Heroes.
It inflates its body with water and shoots poisonous quills using the pressure.

ハリーセン
Water · Poison
Qwilfish is the Balloon Pokémon, a water and poison type that inflates its spiky body with water before shooting poisonous quills at foes. Its Hisuian form can evolve into Overqwil, and our catalog lists 13 Qwilfish cards across 12 sets, including two Hisuian printings from Astral Radiance.
QwilfishOverqwil