Flails in Nightreign are unique weapons that strike through spinning chains, and cannot be parried or deal critical attacks. They have a sweetspot mechanic, which makes head of the weapon deal higher damage on impact than the rest of the weapon. While relatively slow, they offer solid combination of stagger, poise break, and raw damage. Flails can be a good choice of weapon for builds focused on guard counters and poise damage.
NightreignFlails - Nightreign Wiki

Bastard's Stars
Flail • Lvl Required 10
Weapon Skill: Nebula
Imbue the Naturalborn's stars with magic to perform a sweeping strike. This attack leaves a dark cloud of stars in its wake that lingers briefly before exploding.
Unique Weapon Passive: Power of the Lightless Void
Flail which deals magic damage, having been imbued with power by the remembrance of Astel. Formed of the same many-colored star debris that comprised the form of the Naturalborn of the Void.

Chainlink Flail
Flail • Lvl Required 3
Weapon Skill: Spinning Chain
Spins the striking part of a flail at high speed to attack. Follow up with a normal or strong attack to link the momentum of this skill into a successive attack.
A spiked iron tube attached by a chain wielded by Mad Pumpkin Heads. Especially large for a flail, wielding it requires more strength than it does dexterity.

Family Heads
Flail • Lvl Required 7
Weapon Skill: Familial Rancor
Gently rattle the copper heads to summon vengeful spirits that chase down foes. The anguish of a spouse and children invites accursed wrath.
Three bludgeoning copper heads attached to a handle by chains. Signature weapon of Necromancer Garris, the heretical sage. The heads were made to resemble those of his wife and two children.

Flail
Flail • Lvl Required 1
Weapon Skill: Spinning Chain
Spins the striking part of a flail at high speed to attack. Follow up with a normal or strong attack to link the momentum of this skill into a successive attack.
Weapon consisting of a bludgeoning head attached to a handle by chain. The iron ball is spiked and induces blood loss. Blows from this weapon cannot be parried. The charge attack whirls the iron ball around for increased force before striking.

Nightrider Flail
Flail • Lvl Required 3
Weapon Skill: Spinning Chain
Spins the striking part of a flail at high speed to attack. Follow up with a normal or strong attack to link the momentum of this skill into a successive attack.
A flail with two additional bludgeoning heads. Weapon of the Night's Cavalry who ride funeral steeds. The large spikes make it highly effective at inducing blood loss, but also demand higher dexterity to wield.