Dungeon Expansion

Dungeon Expansion is what it says; Dungeon Expansion. The dungeon gets upgraded one by one.
==Post-Eater of Worlds OR Brain of Cthulhu==
"The Evil Presence builds up.." - After you beat Eater of Worlds OR Brain of Cthulhu
After you beat either of those, you get six new enemies. The first depends on what your world is. So if your world is corruption, then you would get the Cannoncurse. Two are hardmode only.
===Pre-Hardmode===
*Cannoncurse -  A cannon which shoots out a cursed flame. In hardmode, it shoots two instead of one. Corrupted only.
*Ketchi - A gigantic cube of red sludge. When hit, it will split into two. Seven hits are required to defeat all of them. In hardmode, it's slightly bigger. It will take eleven instead of seven hits to defeat all of them. Crimson only.
*Blaze Hopper - Hangs from cellings. If it sees you, it will hop to the specific spot you are at. Then it will drop, creating a fire shockwave, and destroying it.. In hardmode, instead of being destroyed, it will come back up, only to shoot out three fireballs in random directions up.
*Locked Mimic - Only pre-hardmode mimic. When opened, it unleashes a Dungeon Spirit which is Purple in Corruption worlds and Red in Crimson worlds. In hardmode, the spirit can summon fakes.
===Hardmode===
*Gigantic Pink-eye: A gigantic pillar made out of Pink Bricks. It's big and it spits out ghastly flare.
*Ghoulish Blue-brick: A gigantic pillar made out of Blue Bricks. It slams its head rapidly.
==Post-WOF==
No message occurs. Only three new enemies are got.
*Lightburst - A pink enemy which shoots out a crystal which explodes into eight crystals.
*Midnight Crawler - A purple enemy which is a worm. It might stop to extend itself, so kill it quick, else it'll get MORE HP!
*Flightbomber - Flies over the player and throws a bomb under them.
==Post-Mechanical Bosses==
All
Another message announces this: "A crawling clank makes the hallways clatter..." This means there's new Mech Versions of the enemies. They replace all Pre-Hardmode (not the FAN-MADE ONES!) Dungeon Enemies, and are way more powerful. If they have Expert-Mode moves, they gain it, but more mechanical.
===Destroyer===
When you defeat the Destroyer, a message announces "Its might curves a way to monsters...".
*Mightycrush - It's the same size as the Eye of Cthulhu. It sometimes jumps to slam you.
*Wall Brawl - Only appears in brick wall areas. It punches pretty heavy.
*Probe Creation - It's five probes. They are immue to everything. The only way to kill them is to give them a damaging effect. It's immue to all effects which don't do damage. When killed, it splits up into five probes.
===The Twins===
When you defeat the Twins, a message announces "You feel like the dungeon is watching your moves closely...".
*Sightwatcher - Enemy which can phase through walls. Does a flamethrower like attack which inflicts cursed flames.
*Brick Rick - Only appears in brick wall areas. It does alot of dodging. Prepare attack it alot.
*Guard of Doom - It acts like a Dungeon Guardian, but you can defeat this kind! For real! (Note: You can defeat Dungeon Guardians actually.)
===Skeletron Prime===
When you defeat Skeletron Prime, a message announces "Risky dangers block your way...". This means Prime Guards appear. Prime Guards act like Dungeon Guardians and are actually dungeon guardians. The only way to get to the dungeon now is to wear the "Tech Pass". However, if you beat Plantera, you no longer need the tech pass, because a message announces "Risky dangers get destroyed...".
*Frightlord - Warps so much that it only has 10 HP. It warps every 0.5 second, firing a Missile of Fright. Don't worry, the missiles are slow moving and can be reflected with a sword hit.
*Bookcurse - Rarely appears. Bookcurse fires out four Water Balls, or rarely, a Magnet Sphere.
*Chiller - If you look at it, you get slown down. 
==Post-Plantera==
It releases its normal announcement but it adds more hard enemies.
===Jungle Enemies===
*Vinespit - Spits out a vine which pulls you in. Drops Ivy Hive, Moss Loop, or Vine Latch.
*Pirahna Sniper - Shoots Pirahnas. Drops Barracuda Bow, Pirahna Gun, or Blowfish Bomber.
*Plague Witch - Wears a plague mask which makes it invincible. Must take off first. Throws out venom shards rapidly. Drops Sick Staff, Virus Launch, or Plague Injection.
==Biome Loot==
From Biome Chests. Basically, there's now a whole set of what class you are.
The dungeon expansion replaces weapons in it with a heart. Enemies now drop the required weapon you need. Hearts are accesories, BTW.
Hearts - Hearts boosts all stats when in specific biome. There's 12 of them.
===Jungle Weapons===
Ivy Hive - On hit, five poison blobs fly out! Also, fire a poison blob! Awesome Melee Sword!
Moss Loop - A boomerang which loops three times before returning to you.
Vine Latch - A mace combined with a HOOK! WHAT IS LIFE! STICK ONTO YOUR FRIENDS! STICK ONTO YOUR ENEMIES! STICK ONTO YOUR FRENEMIES! 
Barracuda Bow - Launch a BARRACUDA! Which farts baby Barracudas.
==Loot==
*Curse Fire - Dropped from Cannoncurse. Fire a cursed cannonball which inflicts cursed flames.
*Sliced Tomato - Dropped from Ketchi. Use to create a clone (max is three). Clone copies all your moves.