Mechanics

Thievery
The hung character in the shop can be attacked. When attacked, it will come to life as a miniboss and attack Isaac. Upon killing the 'shopkeeper', Isaac may pick up any item in the shop for free; the other three items will then disappear.

Map Marking
by Apocalypstic

Pressing X on the keyboard will mark the current room you're in by changing the fill color. You can change the fill color by pressing X again, cycling from red to yellow to green to blue. Pressing O on the keyboard will erase the marking in your current room, and holding the O button for 3 seconds will clear all markings on the whole map. Alternatively, you can left click with the mouse on a room on the map to mark the room and change colors. Right clicking with the mouse will erase the marking, and holding the right mouse button will allow you to drag the cursor and erase markings. This is so you can mark rooms that have tinted rocks or eternal hearts so you can come back later for them, or potentially for other things as well. Only allow marking on rooms you've cleared.

Water and Lava
by Skirdus

As a replacement for holes on certain floors, lava and water would appear. They basically react the same way that holes do. But, if you have a raft, you should be able to cross over large bodies of water (and maybe lava). Also, there can be special water/lava enemies.

Day/Night Cycle
by Gett Numbers

During the game, the mood of the game will slowly go from daytime to nighttime. Every second that you are playing counts as 3 minutes in-game. So when 8 minutes have passed in real-life, in-game, an entire day has passed. At the halfway point of the full day, the enemies change from normal enemies to harder, stronger enemies and the screen pauses saying, "Darkness has fallen." followed by Satan laughing. New enemies will appear at night, such as Bats (faster versions of flies), or sometimes even a Vampire or two. Old enemies won't appear as often, but will sometimes appear in a harder version (champion versions). Each room at night will be dark, sometimes pitch black (if unlucky) but eyes of enemies will glow. When a room is completed at night, the room will light up until daytime. The shop owner will change from selling items for money and instead will sell for Soul Hearts and Hearts (a Devil Shopowner essentially, and no Heart Containers). You can purchase a torch, which will provide constant light for the entire game, but only in the daytime will you be able to purchase it. Bosses will change as well, from being normal to being a Devil version, in which the bosses behave differently and are hardier. Their reward is much greater since Devil Rooms can appear quite often, and a Devil Item will usually spawn as a pickup. The Fallen will appear often at night as well (~35% Chance). One new boss could be Guppy, which only appears at night. The nighttime effect will only happen from the Basement to the Depths.

Holy poop
'''Drops a Treasure (Item) when destroyed. the Treasure would not be a Devil one.''' Has a 3% chance of spawning in every floor.

Abyss Tiles
by RetroMaster

When a Character steps on it, they take 1 heart of damage.

These Tiles are most common to be found in the Depths, Caves, Sheol, Purgatory, Necropolis and in Hell.

The only way to go through these Tiles are by flying over them.

Revamped Luck
What this would do, is give all the items a 1 through 5/10 star rating. Each luck up pushes you up .5 in the ratings. You start at 3 (3 is completely unchanged). If you are higher in the ratings, you get better items. Luck's cap has been increased to 20 and Luck is also now listed in the pause menu.

Similars
What this would do, is if you pick up a familiar, a bomb upgrade, or any type of category of item (besides activated and passive alone), you would find the same type more often until you find them all.

Poisoned
by Unknown

A new status Isaac can receive. Poisoned Isaac is indicated by his hearts tinted green. In this state Isaac takes one half heart of damage every five seconds. This would continue to happen until either Isaac is down to half a heart, or Isaac leaves the room he was poisoned in. Can be caused by enemies such as Gurges and Sloth.

Angel Beggar
by Unknown

The rarest beggar you can find. Spawns in place of a beggar/devil beggar. Unlike the other types, Angel Beggars thrive on soul hearts. When you collide with an Angel Begger you will give a half of a soul heart to him. Another thing that makes Angel Beggars unique is that they has low expectations. Usually around three to five soul hearts at most will satisfy. Angel Beggars tend to drop holy items, such as Halo and Holy Grail.

Philosopher
by BloodthirstyCZ

A beggar with a long beard. When you bring him an eternal heart, he will give you an item and some pickups like bombs, keys, hearts, and coins, and maybe some pills or tarot/playing cards. He wants peace for his thinking, so if you stay too long in his room, he will disappear. If you blow him up, he will be angry and deal 3 hearts worth of damage to you before telporting away. He cannot kill you, however, so if you have less than 3 hearts, you will be borought down to half a heart. He can be found in a regular room, but he is most common in cathedral. He doesn't disappear after spawning his reward, so you can bring him another one for another reward if you wish.

Stat Modifier
by Apocalypstic

Looks similar to a slot machine, but less gamble-like and more mechanical. Will have a random stat symbol on the plate at the top of the machine. Touching the machine will make you lose a stat point in the stat depicted on the plate, and you will have a high chance(60%) to get 1-3 keys and/or 1-3 bombs and/or 3-7 coins, maybe with the possibility for nickels and dimes, though that sounds too excessive. You also have low chance(10%) to get a random item that can be found in the item room, and you have a low chance(20%) of trading the stat for a different stat, or getting an additional stat in the stat you sacrificed(10%). All possibilities are mutually exclusive. You cannot be unrewarded.

Trader
by Qrsyua

Looks like a beggar with a bag and a stand. When you bump into him, he will first trade your space bar item for a different one, if you don't have a space bar item he will take one of you passives and exchange it for another (chooses randomly between passives). If you play him enough times, he will pay out with two items (one space bar and one passive) and disappear.

Crying Kid
by Ribo Zurai

Looks like Isaac crying on the floor, just pitch black and with smoke coming out of him. It will always spawn in a completely empty room, and the music will be muted when you enter it. If you shoot him, he will sometimes spawn a bunch of enemies in the room (like if it was a Gauntlet Room), and if you're lucky, he will disappear and leave a Devil/Angel Room item. Touching him will cause you to be damaged. Exploding him will have no effect.

Customisation
Unlocked after getting the Platinum God achievment.

{C}Since platinum god proves, you beat every challange in the binding of isaac, you now gain the ability to have some additional fun with the game.

You gain a new game option in the main menu, called custumisation.

Here, you can create one personal character and three personal challanges.

In the character creation menu, you have the standard isaac sprite. You can dress him similar to edmund´s game "dead baby dressup", but with more options and an organised menu, people who played that game know what I´m talking about. You can also alter his stats and give him items, but there is a point system to prevent imbalance: you get five points from the start, for more points, you have to take away other stats or gamefeatures. For example, you want Brimstone and The Pact, but together, they cast fifteen points. You either take away stats or remove item rooms, shops, beggars or things like that for this character. (If this whole system gets added, wich is unlikely, the point system needs good balance, you shouldn´t gain 200 points for removing all tresure room or giving your character a constant curse of the lost)

The challanges need a similar balance system, but because they are challanges, not imbages, they should get less points or somethig.

{C}Feel free to edit, I just wanted to post a additional mechanic that could add all the sugjested characters without inflading te character menu with a billion new options. Most of the characters on the fan fiction page sound interesting, but they can´t be added and it would be unfair to add two of them and leave all the others in fan fic nirvana.

Devil Room Surprise
Upon entering Devil room there will be a item that costs no hearts When It gets picked up The satan Statue will rise And the boss fight will begin (identical To sheol satan Fight) The door will fade away and if you win the fight (unlikely) Two free items will appear and a Beam Of light will Be in center of room that will take you to the cathedral and a chest will be in the side of the room (the chest Won't Be there if you have never be in it before) enter it and you will spawn in a room with unlimited keys a Full health pill and 4-10 gold chests (all chests have rare items) a room to the left, it is the ??? Fight, A room to the right champion Red Isaac (starts standing - Two hearts of damage per hit), a room to the top is the DAD! custom boss, And a room to the bottom Which contains Instant Death.

(Devil Room Fight can only happen if You are past Caves/Catacombs)

 First of all... this is a reaally crappy idea. 2 free items at first (from a fight which I can picture would be the end of many runs ) ''with unlimited keys and 4-10 golden chests containing rare items? Let's also not forget that you put an instant death room... Also, I feel like this is more of a new floor idea. You also have 2 bosses on a non-curse of the labrinyth floor, also. Adding all the loot you will get by this idea, you get '8-14 items (I'm pretty sure DAD! and Isaac would both drop items, because you enter The Chest in order to get there. Also, you said you need to get past the Caves/Catacombs. Well, If you got it on the first floor of The Catacombs/Depths, then you miss out on 4/6 items!' (item rooms excluded or included) So, yeah. This is a pretty bad idea :P''



Curse of Paranoia
By BlahTheAmazing

Significantly increases the chances for poop to have eternal flies orbiting them and for normal fireplaces to become orange fireplaces.

Curse of Water
By Undentified

In this curse, speed, range, and tears speed will be decreased (but this will affect the player and every monster/boss). You must complete every normal room in less than 1 minute and the boss room in less than 3 minutes, if you don't, you will start loosing a half of a heart every 5 seconds because you are drowning, stopping at 1 heart. Blue Baby/??? is not affected by this curse.

Curse of Beggar
by Yzexe

No pennies, keys (except golden ones) or bombs (except troll and super troll ones) can be spawned on the current floor for clearing room or in chests. Instead of this, player can buy any items in the shop, infinitely bump slot and fortune telling machines and tribute normal beggars for free until they leave. Player can only have pennies, bombs and keys from these places, from the blood donation machine or from the Box item. Penny counter cannot decrease. Using keys or bombs will decrease the counter as usual. Chests only spawn hearts, cards or pills (or items for golden chests). If there is an arcade room on the floor, it won't contain shell game. Secret room will always contain an item commonly found in the shop. No Greed miniboss can be met on the current floor.

Curse of Plague
By Lazerguy555

This curse makes Flies and explosive enemies (such as Green Nubs) more common. If you are on the Caves or Catacombs, Pestlience has a higher chance of showing up. Fly and diseasish items have a greater chance of appearing, such as Forever Alone or Common Cold are much more common.

Curse of the path
By benyabkn

The map structure will be a single, straight horizontal or vertical line. Player spawns at one extreme of the map, and the boss will be in the opposite one. This curse makes it so you have to go through every room (except if you can teleport) to get to the boss and complete the floor, also means that, both secrets rooms will be harder to locate if the player doesn't have any item that reveals the map.

This curse appears more often in Cathedral/Sheol/The Chest.



Relevant rooms as: Item room, library, shop, curse room, arcade, secret rooms 1 and 2 and sacrifice room will be adjacent to the main path.

Curse of amnesia
By benyabkn

This curse makes enemies to respawn again in a room every time you return to them. As a compensation, the doors from the rooms you completed will always be opened.

Curse of the strongest
By benyabkn

Makes champions enemies spawn more commonly, simple as that.

Buyable Trinkets
Trinkets can be bought from the shop at the same price as a half off item, certain trinkets should also be found in the devil room buyable, and almost always are bought with 1 heart. Some items cannot be bought from the shop or devil room such as Maggy's Faith - by spikeof2012

Cobweb Drain
The more you walk in a Cobweb, the more/less "pulling" it is, and it becomes more transparent to the point where it isn't there anymore. It takes 1 second to drain a Cobweb.