Its description references its original ability in Plants vs. Zombies.
Statistics
Class: Guardian
Tribes: Tree Root Plant
Traits: None
Ability: While in an Environment: This gets +1/+1 and Bullseye.
Set - Rarity: Galactic - Uncommon
Card description
Past job experience includes: Shooing away creepy fog.
Strategies
With
This can potentially be one of the most potent Bullseye plants in the entire game. It has good stats, especially when combined with its ability, and stacks with the abilities of plant environments it is played on. For example, Spikeweed Sector can add 2 damage on top of the damage it normally does, or clear a path to attack your opponent, which makes good use of its Bullseye trait. Pair Pearadise can make another Plantern on that same lane, allowing for more damage overall. When you consider all of the environments in the game, there are many options for boosting Plantern, making it more potent.
Since it is a root plant, it does synergize with Starch-Lord to get more strength and health, making it more of a force to be reckoned with.
If your opponent plays a strong zombie against it, you can play a Team-Up plant, Freeze the zombie, or make it do a bonus attack to prevent Plantern from being destroyed. If they play a weak zombie to sponge Plantern's attack, you can remove the zombie with tricks like Whack-a-Zombie or Berry Blast, or give it the Strikethrough trait via Sun Strike so that it can hit your opponent no matter what.
Against
This plant can be very dangerous if it is in an environment, with it being able to put a big dent on you as early as turn 3. On top of that, it has the Bullseye trait, meaning your Super-Block Meter will not fill at all when it attacks you. Overriding your opponent's environments may remove the extra benefits given by them, but it won't help against Plantern's boost as its ability activates even in zombie environments.
Do not put it in Hunting Grounds, becuse the plant hero can just play another plant to move it away, thus giving you 4 unblockable damage to the face.
Therefore, the best way is to either destroy Plantern so that it can't cause any further trouble, Bounce it with Pogo Bouncer or Excavator Zombie, or move it out of the environment so that it becomes less threatening. You can use powerful zombies to destroy it, but tricks are still the best way to deal with it. The best example of such a trick is Rocket Science. Another option is to use cards like Terrify, Sumo Wrestler, and Rodeo Gargantuar to move it away from environments, getting rid of its stat boosts, although you will have to watch out for Grave Buster and Blockbuster. If you decide to move Plantern, move it onto a heights lane, as environments can't be played there, shutting down any boosting opportunities unless your opponent also has moving cards.
Gallery
Plants vs. Zombies Wiki has a gallery for Plantern.
Guardian class. It costs 3
to play and has 3
/3
. It does not have any traits, and its ability gives it +1
Bullseye trait when it is in an environment. Its closest zombie counterpart is Iron Boarder.
/+1
Freeze the zombie, or make it do a bonus attack to prevent Plantern from being destroyed. If they play a weak zombie to sponge Plantern's attack, you can remove the zombie with tricks like Whack-a-Zombie or Berry Blast, or give it the 
Strikethrough trait via Sun Strike so that it can hit your opponent no matter what.
Kabloom
Mega-Grow
Smarty
Solar
