This character I have she has a magic whip. However I have no idea what powers to give it. I'm open to suggestions.
I once made a story where a character's whip cord was made of magic energy. It could split into multiple threads, and each could attach itself to the base of a person's neck to control his/her body (not mind, though). And given how whip' tips travel faster than sound and create mini sonic booms (the crack of a whip), maybe a wind or sound-based power?
I have a daemon that has a metal and bone whip used for breaking souls. Also works on some armor depending on how heavy it is or if it has some kind of special properties or enchantments. Wonder Woman's lasso made people tell the truth. Though I like @Ulquiorra9000 's idea of having it be a sonic attack of some sort.
This is going to be a long thread I can't think of any powers that a whip couldn't have if the mage who enchanted it were sufficiently powerful and creative: maybe it lets the user fly and carry things, maybe it lets the user read people's minds, maybe it lets the user conjure deadly beasts from the spectral plane, maybe it lets the user turn invisible, maybe it grants the user rapid healing or force protection, maybe it lets the user see through other mages' illusions, maybe it lets the user shapeshift... do you read a lot of comic books? EDIT: maybe it lets the user breathe under water, or talk to animals, or conjure fire, or see in perfect darkness, or run really fast...
Well, it depends on her powers, her personality, the themes of the story, the ability of the antagonists, the amount of magic in the world, the type of magic in the world and a few other variables.
Crack in different ways to use different elements? Like, fire could run down the whip, lightning could crack when the whip does ("You have invoked the Bolt god power!"), or ice could sprout up where the whip strikes the ground.
The word whip, like sword, is also category and not a specific item. You can have a cat-0-nine-tails or a lash, both made for specific tasks. Or, something improvised for the task, like a belt or strap. You can also have something that is whip-like, the Indian flex sword urumi. I would research whips while keeping in mind its use in the context of your story. research + story + imagination = inspiration
One of my UrFan villain protagonists is a military history nerd who's going to be studying Metal magic. I thought that her favorite melee weapons were going to be steak knives, baseball bats, hatchets, and maces. I was wrong
The whip was created to herd animals, so some kind of mind control or invisible force would be thematic.
Mind control or physical control, or both, would be the obvious choices. If you wanted fresher ideas, then perhaps something related to what the whip is made of or how it was made. A drawback of using the whip could easily be that using it transforms the user into someone who's angry and desires to instill fear in others, even if that's not who the person normally is.
Like the others have said the obvious one is mind control. Well a whip isn't really a killing weapon. Maybe it suppresses other people's magic? or drains their life force. Or the whip could be like a magical fuse. You snag the whip on someone and the magic burning or freezing (or poision) could spread visibly down the length of the whip from the handle giving the target a moment to save themselves.
