PAY TO PLAY

PAY TO PLAY is Challenge #24 and was added in The Binding of Isaac: Afterbirth. In this challenge, Isaac starts with 50 coins,, and the. However, every doorway is now an arcade door, and taking any damage will cause Isaac to lose more pennies than can be picked up, similar to when being attacked by Greed. Having 0 pennies will kill him and end the challenge. The goal is to defeat Isaac. This challenge is unlocked by unlocking the Sack of Pennies, done by defeating Isaac with Cain.

Difficulty
Needing money to continue the run causes shop purchases to become much riskier, and extra coins may have to be found in addition to hearts when getting hurt.

The arcade doors in this challenge appear to be "overlaid" on the level's normal doors, even after they have been opened. In most cases, this allows Isaac to unlock and enter rooms that normally require keys (or bombs) with a coin instead. However, certain doors are still "active", and can still damage or block the player, even after being unlocked with a coin. These doors will appear to be normal open doors, despite the effects triggering when attempting to pass through them.
 * Curse Room doorways will still damage the player (without flight and/or shielding) after unlocking them with a coin, despite the absence of visible teeth around the door frame.
 * Challenge Room and Boss Challenge Room doorways will still prevent the player from entering with too few or too many red hearts respectively, even after being unlocked with a coin and appearing to be an open doorway. Unlocking a door for which Isaac has too few red hearts effectively wastes a coin (unless it is planned to return with the right number of red hearts).
 * Both Challenge Rooms and Boss Challenge Rooms can be entered with a coin, but if left they will be closed without the appropriate amount of hearts. This is very convenient as Boss Challenge Rooms will always provide an item from the Boss item pool.


 * Also, the doors to these rooms will appear to be the same as all the other doors on the level. It may be helpful to keep an eye on the mini-map to ensure that health (and coins) aren't needlessly lost to a Curse Room, or waste a coin on a Challenge Room he cannot enter. (Bombing into these rooms appears to leave them unaffected.)


 * Presumably because they hold 0 coins Co-op babies are killed instantly upon entering the game.

Strategy

 * and are fantastic items in this run, as they give Isaac a good amount of coins.  card is useful in this challenge as it teleports him directly to the boss, preventing the loss of any coins.
 * Lucky Rock will allow Isaac to gain more coins simply by destroying rocks. Combined with a means of infinite bombs or any other way to break rocks without a cost (such as ), this trinket becomes invaluable.
 * Store Credit, Credit Card,, , and will all help Isaac obtain items from the shop for free.  Similarly, the  can create free copies of shop pickups.
 * Finding a card early on can potentially max out the coin count, making the run much easier.
 * can be used to get multiple uses out of or.
 * Additionally, if the player can manage to get a, it can be used to get infinite coins, which makes it much easier to win.
 * is very helpful in this challenge, especially if it produces, , or.
 * Counterfeit Penny can increase the value of found pennies. This also means that when damage causes Isaac to drop coins, it is likely to have a net gain once collected. If lucky, this can result in nearly indefinite coins, making this challenge mostly trivial so long as Isaac has a steady health supply.
 * and Swallowed Penny will drop extra coins when hit, likely enough to stop the issue of coin loss from being hurt.
 * can be used in every room to try and generate coins.
 * will keep the coin count at high levels by doubling the value of all pennies found. The earlier it is obtained, the better.
 * gives a chance to earn coins after hitting enemies.
 * can be used to turn enemies into gold that splits into coins.
 * can allow Isaac to exit dead-end rooms, earning him back the coin spent getting in.
 * gives Sack of Pennies a 33% chance to drop a coin in rooms where it normally wouldn't.
 * If the player has many bombs to spare or a renewable source of explosives (such as ), bombing through and out of Secret Rooms can save some coins. Since rooms count as "unlocked" on all sides once they have been successfully entered and cleared of enemies (except for the Shop, which must be exited through the main door to fully unlock), the remainder of the rooms bordering the Secret Room can be unlocked with bombs/explosives instead of coins.
 * Items like and  can help narrow down where Isaac can go and where is likely to just be a dead-end, so they can be valuable purchases from the Shop. The boss room usually appears at a dead-end far away from the spawn point.
 * Shops usually appear farther from the spawn point than Libraries. Both can contain useful items, but the Shop generally has better items for this challenge.
 * Additionally, and  can provide a sustainable amount of money given that each chest opened will likely contain a large amount of coins and other consumables.
 * A combination of Broken Remote with active items that are always charged (or have a recharge time in seconds) can prevent the loss of coins to doors, which can prove to be very effective, but may cause wasted time trying to reach the room desired.
 * When exiting Curse Rooms, it's possible to quickly backtrack into the room to pick up the coins that dropped due to taking damage from the door frame, and then quickly exit once again, without taking damage for the second time. This allows you to conserve coins, and is possible to pull off even with Isaac's starting speed.
 * can kill Isaac by rapidly draining all of his coins.
 * can copy the effects of and help generate coins.
 * Blue Key can be used to completely bypass the money requirement of moving through the floor, at the expense of having to fight twice as many rooms per floor.
 * increases the coin cap to 999, allowing Money = Power to increase damage further, as well as spawning coins in rooms where a room clear drop would not occur.

Reward

 * The pills unlocked are Addicted! and Percs!