Daemon's Tail

Daemon's Tail is a trinket.

Effects

 * All Soul/Eternal/Red Heart drops turn into Black Hearts, if they can.
 * Elements such as Tinted Rocks, Red Chests, Fortune Tellers, Tarot Cards, Little Chad, Bloody Penny, or Blue Fires can't drop Black Hearts. Thus, they will still drop Soul/Red Hearts with Daemon's Tail.
 * The drop chances for every kind of heart are reduced.
 * This means that cleared Rooms, Bosses, Slot Machines, Fortune Tellers, Beggars, Fires, Chests, Red Chests, Poops, Tinted Rocks, Items (Gimpy, Old Bandage, Fanny Pack), Trinkets (Bloody Penny), and Familiars (Little Chad, The Relic, etc) have lower chances of spawning any kind of heart.
 * Hearts that are present upon entering a room for the first time are unaffected by the reduction (for example, the ones found in Curse/Devil/Angel Rooms), but will have their contents converted to Black Hearts.
 * The exceptions to this are particular Super Secret Rooms, which have the effect of forcing all heart drops to be the kind found within them.
 * The V - Hierophant and VI - Lovers Tarot Cards have a chance to drop one heart instead of two. The hearts they drop will not be Black Hearts.
 * If something can drop pickups other than hearts, instead of dropping hearts it will drop its other possible pickups more frequently.
 * This means that these things will keep the same chance to drop a consumable, with an increased chance for drops other than hearts, and less chance for heart drops.
 * In particular, you'll have increased chances for Tarot Cards & Trinkets from Fortune Tellers, Bombs and Keys from Tinted Rocks, Pills and items from Red Chests, and Coins from Poops and Fires, while the rest of the mechanics, like Slot Machines, cleared Rooms, Beggars, Chests, and the Fanny Pack can drop any consumable.

Tips

 * Due to its specific mechanic, Daemon's Tail has no synergy with items increasing chances for Soul/Eternal/Black Hearts to drop instead of a Red Heart, like Mitre, Mom's Pearl, or Bible Tract.
 * Since the frequency of heart drops is lowered, holding this trinket can be dangerous to Isaac if he has numerous Heart containers, as he can easily find himself short on health.
 * This trinket will be more interesting with Blue Baby or Azazel, as they start with no Heart Containers.
 * It can also be useful to get some Black Hearts to avoid Red Heart damage on a floor, and have high chances to get a Devil/Angel Room on this floor.
 * Mom's Pearl or Bible Tract are trinkets who only need to be held to be useful, whereas Daemon's Tail will be more efficient to Isaac if it is frequently held and dropped, in order to get increased chance for consumables from certain mechanics on one side (to counter a lack of Bombs/Keys/Coins, or to get Black Heart protection), and to still get enough heart drops to stay alive on the other side (from Bosses or Familiars).
 * This trinket nearly requires this kind of strategy to pay off for Isaac, making it tough to use as Isaac will have to sort and remember the moments where he must drop or pick up the trinket for the whole floor, as it interacts with nearly every consumable dropping mechanic.