I'm trying to create a feat for one of my players. She likes the whip but i see it have little support in feats. I created this feat, not sure is balanced or too weak... I could have some advice:
Whip Master
* Increase your Strength or Dexterity score by 1, to a maximum of 20.
* When you hit a creature with a whip on your turn, you can use a bonus
action to attempt to grapple the target.
* You can also use a whip to grasp an unattended Small or Tiny object within
your whip’s reach and pull that object into your square. To do so, you must
hit AC 10. Further, you can use the whip to grasp onto an object within
your whip’s reach, using your whip as if it were a grappling hook, allowing
you to use the whip to swing on like a rope. As a bonus action, you can
release the object your whip is grasping, but you cannot use the whip to
attack while the whip is grasping an object.
I like it; I think it works. 
Ty Brodomir.
I'm not that expert but I really think that's good.
For the first "advice": do you mean the Strenght or Dexterity can't go over 20 with that feat?
Just another idea that you could apply to this feat:
If you are already grappling a "dangerous" object, like a potentially bludeoning object or a slashing/piercing one, you can try damaging your enemy with a basic action (consider it as an Attack action), having a bonus damage dice as 1dx (x about 4? or 3?). The damage type depends on the kind of object and on how you are using it.
Sly93 wrote:
I wouldn't give the option for Str increase. Also the feat needs to grant options for disarming and knocking prone. Your player is using a rather underpowered weapon, so this feat should be quite good in my opinion.
Atheosis, im not sure how to do that, the only rules about disarming and trip is on the Battle Master and using superiority dices.
I would suggest talking to your player and getting a good idea of why she wants to use a whip and what she wants to do with it, then from there create a feat that specifically caters to her needs. If her idea is disrupting people from afar, then yeah you'll need to consider trips and disarm, if her idea is Indiana Jones then your original feat should be sufficient.
My only specific critique would be instead of having a specific rules for grasping, releasing, and such use a more general rule such as "you can interact with objects within whip reach (within reason)" maybe explain a few examples to her as well "you can pull small items to you, flip switches, hit buttons, but nothing crazy like picking locks or rolling a boulder."
I think she likes finnese and reach, and i think she is going to take Mage Slayer, and want the whip to grapple mages and the like.
I want to give fun options to the whip (Indiana Jones stuff :D) but i would be nice the trip and the disarm, but i have no idea how to do without superiority dices or ki points. At will can be a little op.
Maybe instead on on a hit getting grapple as a bonus action, what about opting to go for a grapple/disarm/trip from range INSTEAD of doing damage. After all, the wrap/entanglement removes the impact of the end of the whip.
Dara_Kanan wrote:
I think it's okay to deal damage even with a lot of effects/conditions simply beause the whip isn't going to deal a large amount of damage.
Maybe this?
Whip Master
* When you hit a creature with a whip on your turn, you can use a bonus action to attempt to grapple the target.
* You learn the Disarm and Trip maneuver from the Battle Master archetype only with the whip, you also gain one extra supperiority dice or 1d6 in case you dont have. The DC for your maneuvers equals to 8 + your proficiency bonus + your Strength or Dexterity modifier (your choice).
* You can interact with objects within whip reach (you can pull small items to you, flip switches, hit buttons, grasp onto an object like a grappling hook...). As a bonus action, you can release the object your whip is grasping.
Option 2:
Whip Master
* When you hit a creature with a whip on your turn, you can use a bonus action to attempt to grapple the target.
* Also when hit a creature with a whip on your turn, you can use a bonus action to attempt to Disarm or Trip your target. If you do so the attack doesn't cause any damage. The target makes a Strength Saving Throw DC 8 + your proficiency bonus + your Strength or Dexterity modifier (your choice).
* You can interact with objects within whip reach (you can pull small items to you, flip switches, hit buttons, grasp onto an object like a grappling hook...). As a bonus action, you can release the object your whip is grasping.
I like option 2 better. I feel that it is more versatile and less tied into the fighter.