His name is a pun on "brain freeze," which is what someone gets when they consume something cold too fast. This is referenced in the trailer, where he is seen eating an ice cream cone.
This furry fiend combines the best Zombie Pets in the game. He's got everything from Zombie chickens to walrus riders to robotic sharks! Pet-themed Superpowers like Dolphinado and Frozen Tundra help his deadly zoo finish the job.
With
Brain Freeze has the most pet zombies of all zombie heroes, so it's a good idea to use his zombies in pet decks. Cat Lady will get strength boosts from playing pet fighters and Zookeeper will help you boost all of the pets' strength up, making them a powerful army. As if that's not enough, Brain Freeze also has a variety of pet tricks, including Locust Swarm and Dolphinado.
He is also the hero who has the second most Imp zombies, with not only the initial Sneaky Imp zombies, but also Loudmouth, Vimpire, and Kangaroo Rider, allowing him to use an Imp deck with great effects. Toxic Waste Imp and Vimpire make a dangerous combo, as Deadly will destroy any plant Vimpire hurts, and he has the Frenzy trait, thus allowing him to attack again, provided he is not destroyed in combat, and becoming more powerful. Boosting cards such as Vitamin Z will also make them stronger.
Leading both the Sneaky and Beastly classes, Brain Freeze also has the most Amphibious zombies out of all zombie heroes. This makes his zombies very hard to hit most of the time. This way, he can also keep an eye on the aquatic lanes very easily.
Frozen Tundra can also freeze all the plants on the ground, making most of the zombies on the ground safe in that turn, so zombies can destroy frozen plants easily. Also, it can give Cryo-Yeti +2/+2 for each frozen plant. Since it is a classified as a pet superpower trick, it will benefit Cat Lady and Zookeeper.
Brain Freeze's main weakness is that he does not have many tools in order to stop rush decks similar to Template:PvZHLink as he cannot get The Chickening or Weed Spray, so Kabloom heroes can spam weaker plants and win from there. While Fire Rooster, Trapper Zombie , and Sneezing Zombie can help remove them due to their abilities, they cannot stop many higher-health threats at once. Therefore, the closest he can go is to either fight fire with fire, use Deadly zombies, or remove them one by one with his Beastly instant-kills and stat-degraders, which are very expensive. Fortunately, the Zombot 1000 and Cursed Gargolith combo will take care of rushes once he survives into the late game.
Another weakness Brain Freeze has is that without the help of Imp Commander or Interstellar Bounty Hunter, he cannot draw cards at all. Opponents can drain his cards and win from there if he has neither of these cards, so Imp decks could be a viable option to use with Brain Freeze if you prefer spamming zombies.
Against
Most of the time, Brain Freeze will attempt to use a bunch of pets, like Cat Lady and Zookeeper to boost them all up. Try getting rid of his pets as fast as possible, like Cat Lady. If they already got too strong, then use tricks to raise your plant's attack and health. Pet decks have one slight weakness, which is low health. Knowing this, try to whittle down all the zombies' health. If you are playing as a Kabloom hero, you can combine Sour Grapes with Sergeant Strongberry to potentially take all of his pets out at once. Just attacking Brain Freeze isn't really a good idea, as he will raise all his pet's stats, and then outnumber you with his powerful pets. Be careful when playing as Template:PvZHLink, as her superpower will boost Cat Lady and Zookeeper due to Goat being a pet.
Avoid playing important plants on the ground lanes when playing against Brain Freeze, as two of his superpowers, namely Frozen Tundra and Acid Rain, target all plants on the ground lanes.
Vimpires want to suck your chlorophyll! You'll find tons of ways to pump up your Vimpires to take over the game: Toxic Waste Imp, Imp Commander, and Loudmouth among them. Didn't draw a Vimpire? Other Imps will jump in with fake fangs!
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Pets with Cold Noses
Brain Freeze commands an entire zoo! Cat Lady and Zookeeper reward you for your aggressive swarm, while Vitamin Z and Locust Swarm punch through when the lanes fill up. Who knew Fire Roosters had cold noses?
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High Seas High Jinks
Impish shenanigans led by Imp Commander keep the Plants off guard as you buy time for the mighty Zombot Plank Walker to enter the fray.
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Smoke and Lasers
Incoming message from Laser Base Alpha: Requesting Zombies with Frenzy to vaporize intruders (and any Plant Heroes hiding behind them)!
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Secret Saboteurs
Get rewards for hitting your oppoment with Cheese Cutter, Dr. Spacetime, and Ducky Tube Zombie. That's a lot easier when you pump them up with Secret Agent and clear the way with Extinction Event!
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Gallery
Plants vs. Zombies Wiki has a gallery for Brain Freeze (PvZH).
Brain Freeze has the most Amphibious zombies among all zombie heroes.
This is because he leads the Sneaky and Beastly classes, the only zombie classes with Amphibious zombies.
When fighting Brain Freeze in Missions, he sometimes uses Eureka, which is Professor Brainstorm's signature superpower. This is most likely a bug.
Prior to update 1.16.10, Brain Freeze was the only zombie hero that can freeze plants in Plants vs. Zombies Heroes, by using his signature superpower.
When Brain Freeze enters the battle at the beginning, the ice statue he breaks out from has the same pose resembling a famous still supposedly made by a Bigfoot from footage taken during the Patterson-Gimlin film. He is also seen in this pose in his official artwork.
Sneaky and 
Beastly classes. His signature superpower is Frozen Tundra, which gives all plants on all ground lanes the 
Freeze effect.
Sneaky, 
Deadly will destroy any plant Vimpire hurts, and he has the 
Frenzy trait, thus allowing him to attack again, provided he is not destroyed in combat, and becoming more powerful. Boosting cards such as Vitamin Z will also make them stronger.
/+2
for each frozen plant. Since it is a classified as a pet superpower trick, it will benefit Cat Lady and Zookeeper.
Brainy
Crazy
Hearty
Sneaky