She doesn't have any traits, and her ability destroys any zombie that does damage to a flower plant, including her, instantly after. This ability activates even if the damage destroys the flower and persists until all Briar Roses are removed from the field.
She is based on a rose, a woody perennial flowering plant of the genus Rosa, in the family Roseceae, or the flower it bears.
Her name could be a reference to Sleeping Beauty, also known as Little Briar Rose, a classic fairy tale written by Charles Perrault and the Brothers Grimm. A "briar" is a prickly scrambling shrub or plant, such as a wild rose.
Her description is a reference to the quote, "Don't mess with the bull, young man. You'll get the horns." from the movie The Breakfast Club.
Statistics
Class: Solar
Tribe: Flower Plant
Traits: None
Ability: When a Zombie hurts a Flower, destroy that Zombie.
Set - Rarity: Premium - Legendary
Card description
"You mess with the rose, you get the thorns!"
Update history
Update 1.2.11
Name change: Rose Thorn → Briar Rose
Update 1.12.6
Ability change: No longer activates if a zombie that damaged a flower has already been destroyed in combat.
Update 1.16.10
▲ Sun cost change: 6 → 4
Rarity change: Super Rare → Legendary
Update 1.22.12
Animation change: Legendary shine added.
Update 1.30.4
▼ Sun cost change: 4 → 5
Strategies
With
Briar Rose has horrible stats for a 5 plant, but her ability is what makes her one of the most feared plants in the game.
While a flower has to be hurt to activate it, she is able to destroy any zombie regardless of strength or placement, which is essentially a cheaper and more versatile instant-kill compared to others like Lawnmower and Whack-a-Zombie.
She works very well with ramp cards such as Solar Winds and Sunflower Seed as like other similar cards, the earlier she comes out to play, the better she has an impact on the field.
The more flowers you use with this, the better she gets. As long as Briar Rose is in play, even weak flowers like Bellflower and Sunflower can be used as cannon fodder for dangerous threats like Shieldcrusher Viking, Wannabe Hero, Zombot Sharktronic Sub, Zombot Battlecruiser 5000, and even Gargantuars' Feast. Even on her own, Briar Rose is still very effective since she is basically a hard removal card with a body. However, be wary of tricks, and now that her cost has been increased, this tactic may not be as viable.
The hero who can use this plant to her maximum potential is Wall-Knight, since he has access to Steel Magnolia, which increases other plants' health so they can withstand more hits, Poppin' Poppies, which creates 3 Lil' Buddies, spelling doom to any attacking zombies in the same lane as Poppin' Poppies and next door, and Red Stinger, which can protect Briar Rose with his high health.
She also works well with Soul Patch due to their combined abilities being capable of destroying any zombie that attempts to attack you. Chompzilla may not be as efficient in the health-boosting side of things, as she will have to rely on cards such as Fertilize to do so. However, she does have access to Umbrella Leaf, which is not only a flower herself, but it will also allow Briar Rose to have immunity to her biggest weakness - tricks.
Against
Briar Rose is a very dangerous plant if the field is full of flowers. But since her ability only activates against zombies, you are free to play tricks and environments at your disposal. The best method of dealing with Briar Rose is Knockout for Hearty heroes, as it destroys all plants in any lane with 3 strength or less. If you don't have one, resort to slightly less effective ones like Cakesplosion or Locust Swarm to dispose of her quickly.
As The Smash, you can surprise the opponent by using Slammin' Smackdown to instantly destroy her only for 1 brain, or Knockout for 3. He can also use hard removals from both his classes to take her out. But if you really have no alternative other than to directly attack Briar Rose, it is best to destroy her in one hit. Another option is to wipe out the other flowers first so that Briar Rose may wreak less havoc.
Weed Spray or The Chickening could do the job, but they may not be able to destroy all (or even most) of the flowers due to both of them having limits. Barrel of Deadbeards is also a viable choice, as Briar Rose's ability only affects it, leaving the other zombies unharmed and making a Captain Deadbeard as well. But either way, bonus attack cards are worthless against her, as the zombie will just be hastening its doom.
Rustbolt can use Shrink Ray to prevent it from damaging you, although he should quickly remove it afterwards.
As a Sneaky zombie hero, you can use Deadly zombies to quickly dispose of Briar Rose. Alternatively, Super Stench and Laser Base Alpha combined with either Barrel of Deadbeards or Fireworks Zombie (only as Impfinity) can be used to clear all plants, including her. However, you must also note that doing so will wipe out all your zombies as well, unless you have no zombies.
It's extremely worthwhile to Bounce Briar Rose - her high cost makes replaying her very punishing for your opponent, and if your opponent relies on this to win, they won't have time to set this back up. Try Zombot Stomp to bounce this and every other plant on the ground - replaying everything can be expensive and will put a serious dent in your opponent's strategy.
As damaging tricks are not affected, Impfinity can also try Zombot Sharktronic Sub, and the Crazy class' tricks should do well if they are not shielded.
Yet another dangerous strategy is to use her ability to your advantage and combine her with zombies with powerful "When Destroyed" abilities. A good example is Gas Giant, who will do 5 damage straight to the plant hero. Your opponent will be unlikely to anticipate these fighters and will suffer as a consequence.
Gallery
Plants vs. Zombies Wiki has a gallery for Briar Rose.
Solar class. She costs 5
to play and has 3
/4
.
Hearty heroes, as it destroys all plants in any lane with 3 strength or less. If you don't have one, resort to slightly less effective ones like Cakesplosion or Locust Swarm to dispose of her quickly.
Sneaky zombie hero, you can use 
Deadly zombies to quickly dispose of Briar Rose. Alternatively, Super Stench and Laser Base Alpha combined with either Barrel of Deadbeards or Fireworks Zombie (only as Impfinity) can be used to clear all plants, including her. However, you must also note that doing so will wipe out all your zombies as well, unless you have no zombies.
Crazy class' tricks should do well if they are not shielded.
English
Simplified Chinese
Kabloom
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Smarty
Solar