Jungle

The Jungle is mud, jungle grass, hanging vines, Bamboo and mahogany trees, with pools of water everywhere and a dark green sky. It reads as scenery and plays as a difficulty spike. Its enemies carry noticeably more health and hit harder than anything else on the surface at the same stage of a run, and the pools hide things that will kill you while you are swimming and cannot swing properly. Silver or Tungsten armor is a sensible floor before you walk in.

The Jungle always generates on whichever half of the world does not hold the Dungeon or the Snow biome, and it shares that half with the Underground Desert. Sometimes it generates within sight of spawn, occasionally near the middle, and either way locating it hands you the rest of the world layout for free. Mahogany regrows on jungle grass by itself with no replanting, so Rich Mahogany never runs out once you can safely reach it.

The strongest early move in the Jungle involves no combat at all. Jungle Crates draw from the same loot pool as the Ivy Chestes buried in the caverns below, and the surface has large open pools sitting right there in the open. A Reinforced Fishing Pole and a stack of Enchanted Nightcrawlers is all the tackle you need, and you can wall yourself into a small box so nothing reaches you between casts.

That route hands you things like the Anklet of the Wind and the Boomstick before your first boss, with no chasm diving, no cave crawling, and no fight you were not equipped for.

When Hardmode starts, the aboveground Jungle becomes one of the deadliest places in the world and one of the least rewarding. The enemies combine attacks in ways that end a run in a hit or two on Expert and Master, and the loot list is thin: the Uzi, and Turtle Shells that do nothing for you until you have beaten the mechanical bosses and can mine Chlorophyte Ore.

The Jungle Key is the exception worth planning around. Any Jungle enemy can drop it, and it opens the Dungeon's Jungle Chest for the Piranha Gun once Plantera is down. Farm it before you kill her, because on Expert and Master every enemy in the world gets stronger the moment she dies.

Corruption and Crimson both convert jungle grass, and an infected Jungle stops being a Jungle. Its enemies stop spawning, Life Fruit stops growing, and the materials you need for the next several tiers dry up with them. The surface strip is the most exposed part of it by far.

The Underground Jungle is enormous by comparison and much harder to lose, which is the argument for putting your Jungle house and Jungle Pylon down there rather than on the surface. It also drops you next to where your Plantera arena will eventually go, which saves a long walk later.

Jungle Grass Seeds on Mud Blocks will start a Jungle anywhere in the world, though jungle grass creeps far more slowly than ordinary grass and you should plan on waiting. The biome check wants 140 related tiles, with one more than that before the background changes over, and jungle plants, Lihzahrd Brick and Hive blocks all count toward the total alongside the grass itself. That last detail makes a rebuilt Jungle cheaper than it looks if you have hive blocks lying around.