An tightly woven whip of blackened vines with a corrupted Wyvern stinger at its tip. This whip is light yet strong enough to hang from.
You have a +1 bonus to attack and damage rolls made with this magic weapon.

Dan's Reasonable Ideas
- Damage: 1d6? 2d4? (1d4 piercing for the normal whip + 1d4 poison one for the stringer?)
- Extended reach of 15ft (/20ft at Disadvantage?)
- Chance of poisoning on Critical Hit (DC12 Con save) or just an additional poison damage die?

Whip Abilities
(I figure these could either be: Used as a Bonus Action / Used instead of Damage [which, I think is the fairest way to balance this with the abilities] / Used in place of a second attack / Used as charges... Though the charges don't make as much sense with most of these abilities)
- The whip can be used to Grapple an opponent within range. No other attack can be made while the grapple is maintained.
          - If an opponent is grappled, success on additional grapple checks pulls them 5ft toward you. (10ft if they are size small or under, DIS on Large Creatures, cannot be used on anything bigger)
          Suggested Balance: - Opponent has advantage on grapple checks against the whip on their turn if there has been no further effort to restrain them.
- The whip can be used to Trip an opponent. A successful grapple check knocks the opponent prone (maybe to balance, disadvantage on large creature, and anything bigger is immune?)
- The whip can be used to Disarm an opponent (with the same size restrictions as before?)
- The whip can be used to Shove an opponent (Size restrictions)
- The whip can be use to Pull an object not being gripped (on the ground / Hanging from a belt / etc) and within range towards you. The object lands at your feet.
- Reaction: The whip can be used to grapple in place of an Attack of Opportunity.

Just before I get into the more silly ideas. Another idea to simplify would be to just use additional damage. In that case, I'd suggest a few charges in the Stinger that can do additional poison damage/condition on a successful attack (ie, one charge is an additional D4/6/8 damage, or a chance to poison). Personally I prefer abilities, but I also don't want to be metagaming and being able to do everything. These are all the "sensible" ideas, the following are the more silly ones. I'm sure somewhere in here is a good mix to get a balanced weapon.

Dan's Silly-But-Fun Ideas
(The following ideas are my more ridiculous ideas that I don't expect would work as per our discussion, but just for the fun of imagining the possibilities)
- Whip Crack (maybe charges?): The whip cracks near a single target's head(s), disorientating them. Their next attack is at disadvantage if they fail a 12DC Wisdom Save. The whip crack can be heard over 100ft away.
- Deflect Missile (I know, but wouldn't it be cool?): As a reaction, the whip can be used to knock an arrow out of the air if it passes through its field of range. (DEX check against Archer's Attack Roll? - Again, this idea is ridiculous, I just wanted to give you a laugh at the thought).
- Precise Crack (Just for fun): The whip can be used to extinguish a candle within range, pop a balloon, knock a cigarette out of someone's mouth, or strike the hair off a fly's arse (which is to say, strike within a space no larger than 2cm sq.)
- Tipped: During a Short or Long Rest, the tip may be changed to modify the damage output/type. Material may be crafted (such as silver tips, etc) - Discuss with DM.

Proficiency with a Whip allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Damage: Poison, Weapon Property: Light, Weapon Property: Finesse, Weapon Property: Reach, Poisoned, Grappled, Prone, Damage, Combat, Finesse, Reach, Slow