You should look at Mork Borg if you don't already know about it; it was because of a Twitter exchange with them that I've thrown together this table of random flails.
Bear in mind, the flail familiar to us from consumable media is not necessarily a replicable historical object (see The Curious Case of the Weapon That Didn't Exist* and The Case Against the Medieval Ball and Chain).
I'm not an expert, nor a mall ninja, so I'm not making any claims to historicity, to realism or to simulationism.
Flails in Game.
- will have a feature like Awkward, Clumsy, Heavy or even all three
- primary special: ignore shields (flails strike over or round them)
- optional/secondary special: chains can be used to snare & disarm
- on a fumble, you definitely hit yourself
1st d6 (1-2) 2nd d6:
- Death Tolls Twice: double-ended flail; wield it like a quarterstaff, if your Strength is 15+.
- Whirligig: triple-headed throwing flail; whirl to wind it up, then hit the release.
- Flagellant’s Friend: three slungshot on a rod; subdual damage.
- Flagellant’s Favourite: nine hooked chains on a haft.
- Flagellant’s Fine Fellow: spiked iron paddle on a short chain, heated red hot; stout, two-handed haft.
- Star of Dawn: not a morning star.
1st d6 (3-4) 2nd d6:
- Hunter’s Belt: not a triple-headed morning star.
- Goddess of Love: not a morning star with a hollow head for burning sulphur; three-headed version is The Triple Goddess.
- Tresses of Medusa: three, six or nine chains on a haft; spiked balls are hollow as venom reservoirs.
- Throne of Skulls: triple-headed skull flail with spring-loaded snapping jaws.
- Dragon’s Neck: flanged/spiked head on a telescopic chain; reach weapon or actual hookshot-from-Zelda, depending on your campaign.
- Meteor Hammer: double-headed long fighting chain; flanged/spiked heads forged of starmetal/meteoric iron; cage heads for combustible material.
1st d6 (5-6) 2nd d6:
- Ogre’s Choice: 3+ sword/axe blades on short chains; two-handed haft, Str 15+ to wield. Stupid idea; looks intimidating.
- Murther of Crows: double- or triple-headed straight-bladed sickle flail; two-handed haft.
- Gentleman’s Flail: bafflingly petite quadruple-headed spiked flail; hollow handle for drinky-poos or secret notes from/to your beloved.
- Shooting Star: unassuming single-headed one-handed flail with a pistol built into the haft.
- Shield Splitter: enormous two-handed single-headed spiked flail, Str 15+ to wield; anytime a shield foils an attack from this, it has to save vs. crushing blow.
- People’s Friend: repurposed agricultural flail; studded with nails; dipped in shit.
*The Weapon That Didn't Exist.
- Only available in post-medieval time periods, this is an apparently ordinary flail, morning star or chain weapon.
- Once claimed, it can only be relinquished on your death or by a quest, remove curse or similar.
- It does not exist, has no encumbrance value and is completely undetectable except when you are wielding it in combat; it is always your primary melee weapon and appears in your hand. You can still wield other weapons in your off-hand.
- If you attempt to put it down or pass it to someone else, it vanishes until you next wield it in combat.
- If you are disarmed, it vanishes as it leaves your grip but will be in hand at the start of the next combat round.
Edit: Table removed for wider browser compatibility.