The phrase "Deep Sea Quarterly" mentioned in his description may be a reference to Great Ocean Quarterly or Paper Sea Quarterly, both being titles for ocean-related magazines in real life.
Statistics
Class: Beastly
Tribes: Monster Gargantuar Zombie
Trait: Amphibious
Abilities: None
Set - Rarity: Premium - Super-Rare
Card description
Has every single issue of Deep Sea Quarterly, but rarely has time to read them.
Update history
Update 1.16.10
▲ Strength change: 6 → 7
▲ Health change: 6 → 7
Rarity change: Rare → Super-Rare
Update 1.30.4
▲ Health change: 7 → 8
Strategies
With
With a massive 7/8 for just 6, Deep Sea Gargantuar can destroy tough plants while surviving at least an attack from one. He also has the Amphibious trait, which makes him especially dangerous on aquatic lanes since most Amphibious plants don't have enough strength to destroy him in two or less attacks. If he gains additional traits from Wizard Gargantuar and/or Smashing Gargantuar, or has his stats boosted, Deep Sea Gargantuar can easily end the game in your favor.
However, because of his high cost, this zombie can only be played later in the game. By then, your opponent can also use powerful cards to deal with Deep Sea Gargantuar; even Solar Flare, Chompzilla, and Captain Combustible, the three heroes with no Amphibious plants, have their ways to counter him. While you could play Gargologist to play him at least two turns earlier, this combo can primarily only be played with The Smash.
Against
This zombie is one of the strongest Amphibious zombies and should be removed quickly. However, using plants to one-shot him is not recommended because the options are extremely limited (Guacodile and the moving card + non-Amphibious plant combo), and those that can do the job cannot survive an attack from Deep Sea Gargantuar. Instead, just like any zombie with massive stats, hard removal is the best option. While Squash is good, Shamrocket is an even better choice, being able to destroy Deep Sea Gargantuar for a cheaper price. Another strategy is using transforming cards (The Great Zucchini, Transmogrify, Goatify) since you get to deal with a much weaker zombie. While Rose and Citron have instant-kills themselves, the last two examples are a lot cheaper than any instant-kill; also, the first example is the only one available to Green Shadow and Nightcap if they wish to neutralize him before combat.
Gallery
Plants vs. Zombies Wiki has a gallery for Deep Sea Gargantuar (PvZH).