Plantera

Plantera is a Hardmode Boss that can be fought after The Destroyer, Skeletron Prime, and The Twins have been defeated. Once you defeat your last Mechanical Boss it displays this message, 'The jungle grows restless'.

Summoning
After all three (only one of three in Console version) of the mechanical bosses have been defeated, one or more Plantera's Bulbs will appear somewhere in the Underground Jungle. Destroying one of these bulbs requires a Pickaxe or a Drill, and upon doing so, Plantera will spawn.

Attacks
Plantera moves through blocks as well as using long vines to grapple foreground blocks in order to move. Its grapples cause damage on contact, and can be killed individually, but only its main body needs to be killed in order to defeat Plantera.

First stage
Plantera creeps after the player, firing seeds and flower petal projectiles. These fire more rapidly as Plantera takes more damage. Plantera also begins to spit large, bouncing spiked balls after taking a certain amount of damage.

Second stage
Once Plantera is brought down to half its original health, it changes to its second form, with its pink bud falling away to reveal a thorn-filled mouth. In this form, Plantera moves quicker, and primarily attempts to make physical contact rather than fire ranged attacks.

Additionally:
 * It sprouts mouths that are attached via additional vines (called "Plantera's Tentacles").
 * It begins releasing floating pink spore projectiles that drift toward the player, similar to the spores released by the Giant Fungi Bulb.

Enraged stage
Plantera only becomes "enraged" if it follows the player out of the Underground Jungle, for instance to the surface. This causes it to gain significantly more damage and movement speed, and will attempt to remain directly on top of the player, causing constant damage.

Aftermath
When Plantera is defeated for the first time, it will always drop a Grenade Launcher with Rocket I's for ammo, as well as the Temple Key. A Temple Key drops each time Plantera is defeated thereafter.

The Temple Key allows access to the Lihzahrd Temple and Golem Boss, who drops Beetle Husk for crafting Beetle armor. In addition, the Temple Key can be combined with Biome Key Molds to craft keys for access to Biome Chests.

The Cyborg NPC becomes available, and the Truffle begins selling the Autohammer, used to craft Shroomite Bars for Shroomite armor and other endgame items. The Traveling Merchant will begin selling the Pulse Bow.

A message saying "Screams are echoing from the dungeon" will appear, as new, more difficult enemy types will begin to spawn in the Dungeon, which drop new weapons, accessories, and other useful items. Dungeon Spirits will begin to appear when Dungeon enemies are slain, which drop Ectoplasm, a new crafting material that offers access to the Pumpkin Moon and Frost Moon events, as well as the Spectre armor and tool sets.

Tips

 * Excavate a sizable area to allow easier dodging before summoning Plantera.
 * Plantera's Bulb can spawn in player-made Jungle Biomes, which can provide a slightly easier way to fight Plantera.
 * Line up 2 teleporters ~50 blocks away from each other in two small separate rooms with a tiny hole. When Plantera is summoned, fire at it using a Megashark or Clockwork Assault Rifle. When it gets too close, teleport to the other room.
 * To find Plantera's Bulbs more easily, press M (for the map). Zoom in and look for a pink/purple rectangle. Put your mouse over the rectangle and it should say Plantera's Bulb.
 * Narrow Passages slow Plantera as it takes more time for it to grip the surrounding terrain. Use of the Death Sickle in the narrow passages will result in up to 3,000 max damage in a 30-40 tile tunnel.
 * If you have already beaten the Golem, the Stynger is very effective.
 * Using a Golden Shower, Ichor Bullets or Ichor Arrows may be useful as the debuff they inflict lowers its defense.
 * Using Dart traps or Super dart traps can be useful.
 * In multiplayer, build a house with a bed near Plantera's Bulb. Make all players spawn at the bed, so you will be sure to kill it, as Plantera does not despawn unless if all players die and spawn in other places, hence the bed in the house near the bulb.
 * If you have beaten Duke Fishron. His Flairon is effective due to the fact that it is a homing projectile, unaffected by gravity, no mana or ammunition cost.

Trivia

 * The name "Plantera" is a word play of the American metal band Pantera, which is Redigit's girlfriend's favorite band.
 * Plantera drops "The Axe", which looks similar to the Washburn and Dean electric guitars often used by late Pantera guitarist Dimebag Darrell.
 * Plantera's boss music features heavy electric guitar use.
 * This boss bears a resemblance to Kalle Demos from The Legend Of Zelda: The Wind Waker, as well as Biollante from the Godzilla movies. Both are giant flower creatures who eventually transform into a much more dangerous form with gaping, tooth-filled mouths.
 * In Swedish, the word plantera means "to plant".
 * As the console 1.2 update, the new saving icon is one of the spiked ball that Plantera shoots. Prior to this update, the Thorn Chakram was used as icon to save.
 * Plantera is among the hardest bosses in Terraria (the Frost Moon, Pumpkin Moon, and Duke Fishron are more difficult).
 * Plantera may be a reference to Audrey 2, a character off of Little Shop of Horrors, and the main antagonist in the film.
 * Plantera may be mechanical, as the chance to drop the Grenade Launcher, attract the Cyborg to move in, and the fact you have to defeat 3 mechanical bosses to spawn the bulbs.