Nearly all bosses have their own item drop (similar to Steven or Gish). These have a chance to replace the normal room reward, and excludes most bosses that do not normally provide room rewards when killed.
Delirium now drops an Eden's Blessing when killed.
The four horsemen bosses no longer drop Cube of Meat or Ball of Bandages when killed; these have been moved to other pools. Once collected, these items have a chance to replace other pedestals until four have been picked up (forming a full-sized familiar).
Most collectibles that permanently increase Health have been removed from standard pools, and are now only rewarded for killing the floor boss without taking damage.
Changes: Contains all varieties of 'holy' items, excluding those in the Library or Health Upgrade pools.
Changes:
Battery Beggars reward items related to batteries or electricity.
Bomb Beggars reward items related to bombs and bomb upgrades.
Coin Beggars reward items related to money or coins.
Crane Games reward items from all other beggars, excluding Demon Beggars.
Demon Beggars reward low-quality items from the Devil Room pool .
Key Beggars reward items related to keys.
Rotten Beggars reward items related to rot and death.
Shell Games reward items related to poop or flies.
Changes: Contains items that are directly related to Isaac's stats (including Health).
Changes:
Eternal Chests contain low-quality collectibles from Angel rooms.
Gold Chests contain low-quality collectibles from all pools.
Red Chests contain items that resemble parts of dead animals, as well as low-quality collectibles from Devil rooms.
Wooden Chests contain items that resemble chests, such as Isaac's Tomb.
Changes: Contains low-quality collectibles from the Devil Room pool, as well as those that are related to Curses (such as Black Candle).
Changes: Contains all varieties of 'evil' items, excluding those in the Library or Red Chest pools.
Changes: Contains all varieties of books and scrolls.
Changes: Contains all Zodiac and similar Astrology items.
Changes: Contains high-quality and similarly strong collectibles that are unavailable in other pools.
The Ultra Secret Room has an increased roster of such items.
Changes: Contains all items from the Treasure room, as well as a select few Familiars.
Items now have a variable price based on Quality.
Hearts, cards, and pills now have a variable price based on current stage.
Sacks and Batteries now have increased prices.
Changes: Contains items with special effects that are not covered by other pools, 'weapons' that alter Isaac's tears, and select familiars.