WingedKagouti: It reads/sounds
a lot worse that it actually is. There's plenty of time to goof around, mess up, take screenshots, go fishing, build castles, rearrange your chests, search for Strange Plants and so on. And if you want a breather you can just make a new world.
Unless you get truly unlucky with where the Corruption/Crimson hits, it will take quite a while (think a couple of real life weeks of actual gameplay) before your Jungle is in danger of being permanently destroyed. And once you do defeat Plantera, the speed the hostile biomes spread with will decrease noticably.
The first day/night cycle or two in hardmode are actually less dangerous than the first few day/night cycles in normal mode the first time you played (though there is still a very real risk of dying). Just use the time to learn how the new enemies react and try to assess how to handle the old and new Corruption/Crimson. One way of ensuring your housing will remain valid if it is in the path of the spread is to plant some Hallow around it.
Then again, if you do go and break every single Demon/Crimson Altar in your world as soon as you can, things might get a bit hairy. If you just break 3-6 you'll be fine (remember to deal with the enemies that spawn before breaking a new altar). And if you delay breaking altars, you'll also keep the mechanical bosses and pirate invasion from spawning randomly.
Also, making your Hellevator 4 wide can help to contain the Corruption/Crimson to one side of the world.
Thanks so much for taking the time to give me that answer. And Thorfinn, I'm way ahead of you. First thing I do when I get into the dungeon is take out all the spikes....and them use them to cover my house. :P
As Thorfinn pointed out Hardmode is harder but it sounds alot worse then it really is. Especially now since it got rebalanced in 1.2 and 1.3. Back when it was first introduced it was rough, I actually stopped playing it after 1.1 because how rough and just tedious it was. back then you had clowns that spawned during blood moons that can blow your base to bits which thankfully got nerfed so while they still toss bombs they have the same effect as gernades, so they only damage the player/npcs and not actual tiles.
Thankfully now it's not so bad, yeah you still got more powerful mobs during bloodmoons like possesed armors, wraiths, giant eyes that are like mini eye of Cthulhus which when at half health will spin and will then have a set of teeth, those clowns and on full moons werewolves. But really not as bad as it was when hardmode was first introduced as those wraiths would spawn constently in my base and those clowns would blow half of it up..
Save for that, it's just like starting the game over again and like pre-hardmode most of the really harder stuff doesn't really happen till you trigger it. Like Pirate Invasions, like goblin invasions won't happen till you either hit a certain point progress wise, hardmode bosses don't spawn unless you summon them or in the case of Plantera, The Golem, the Lunatic Cultist and the Lunar event, till you trigger them like Plantera's bulb won't appear in the underground jungle till you killed all three mechanical bosses first, you can't awaken the golem till you killed plantera the cultists won't spawn till the golem has been slayed, the lunar event won't trigger till you killed the head cultist and the moon lord won't appear till you finished the lunar event.
Now you can cause certain things like pirate invasions and mechanical boss fights to start earlier if you end up smashing more then a set number of demon/crim altars which you need to do to seed the world with three of the new hardmode ores, there is also another penalty for doing that but I'll touch on that further down.
But the Pirate invasion isn't that tough, the worst mob you will deal with is the captain who takes alot of hits and doesn't get knocked back easily the only other mob that gives me as much headaches as him is nailhead in the post-plantera version of the solar eclipse.
As for the Corruption/Crimson killing your jungle thing never happened to me ever, the key thing is if you have corruption/crimson by your jungle just block it off with hallow via holy water(10 bottled water and 1 hallow seed) and it will stop as it won't spread passed hallow and then later you can remove both completely with the clentemiator gun. Also make sure you don't kill the wall close to where your jungle would be on the surface that way you got plenty of time to block the hardmode corruption/crimson from reaching your jungle pending it's to the right, if it's too the left you don't have much to worry about unless you hallowed biome spawned on top of the jungle then you will more then likely have to create a new one manually via holy water on the surface and underground and a lot of waiting for it to spread on it's own.
And be careful how many altars you destroy as every one you smash will cause the game to place a random patch of corruption/crimson or hallow in your underground. Usually I smash no more then 6.
Oh and if you haven't stock up on bottled waters, regular mushrooms and dayblooms as well as build a good sized arena with a sky walkway attached this will make taking down the mechanical bosses easier just use the arena for the destroyer and prime and the walkway for the twins since the best thing to do with the twins is run backwards while firing on them and try and take out the green eye first. it's pretty easy just start blasting at the green eye to bait him into chasing you and keep plugging away at him with a megashark or uzi and crystal or cursed bullets. The Destroyer I just make sure I have a cross(a drop from the mimics) reforged to warding(and maybe reforge a few other accessories to warding as well), make a phasesaber and reforge that to legendary and bash the hell out of him while making sure to move around enough so I don't get hit by it's head nor let it constrict itself around me. Also make sure you craft some Regen and iron skin potions before each fight they help(hence the make sure you have plenty of daybloom, mushrooms and bottle water handy tip) also the magical harp is also a good weapon to use pending you killed the twins first as you need souls of sight to make it.
Skeletron prime, just keep moving and blasting at him and avoid getting hit by it's head when it does that spinning attack. Wings, cloud/sandstorm/fart/blizzard/typhon in a baloon, specter boots and a pair of at least demon/angel wings help.
