Dying as Tainted Jacob after being touched by Dark Esau and carrying this item will respawn him in the previous room in his lost form.If Tainted Jacob takes this item after being touched by Dark Esau, he will return to his previous Red Heart total upon reaching the next floor.But if they die, both are resurrected with one Red Heart Container. If Jacob and Esau take the item, only the brother who takes it will be set to one Red Heart Container on pickup.This item counts as 9 items, so if Isaac is trying for an early portal to The Void after beating Mom, this will significantly boost the progress closer to 20 items.Only the first dead cat counts toward becoming Guppy. Additional Dead Cats can be picked up during a run, increasing lives well past 9.The effects of the D4, D100, Missing No., or a 1- or 6-pip Dice Room will not remove the lives granted by this item.The lives are added after the "picking up an item" animation has ended, so characters that die while the animation is playing will not be revived by this item.If picked up as The Forgotten, his Bone Hearts are reduced to 1 but The Soul's Soul Hearts remain unaffected.Picking this up as The Lost would not show the number of remaining lives, but will still function.Dead Cat is 3rd / 4th in this order after Soul of Lazarus, 1up!, and Lazarus' extra life. Resurrection items activate in a set order.Unless either of them have immediate access to an HP Up item, taking Dead Cat is usually detrimental. Taking Dead Cat as Keeper or Tainted Keeper will reduce their total number of Coin Hearts to one, meaning they will die upon taking any damage at all.This will result in Dead Cat reviving Isaac back inside the Devil Room. To take multiple Devil Deals, buy a Devil deal item then quickly leave the room before the "item get" animation finishes.Other Devil Room items can be bought without the necessary number of Heart Containers at the cost of one of the many lives Dead Cat provides.Buying Dead Cat when at 1 Heart Container essentially obtains the item for free. Taking Dead Cat with 1 or 2 Heart Containers won't kill Isaac because it will set his number of Heart Containers to 1 immediately, saving him from the death that would have resulted from having no Heart Containers.Collecting three items from this set will transform Isaac into Guppy. When Isaac has lost all of the lives provided by this item, the Guppy familiar will disappear.The head of Guppy begins following Isaac like a familiar upon pickup but doesn't do anything.Any active items in Isaac's possession will lose all its charges.Isaac respawns in the previous room with 1 Red Heart container.Does not remove Bone Hearts unless picked up as The Forgotten.Does not remove Soul Hearts or Black Hearts unless picked up as ?, The Soul, Dark Judas, Tainted Judas, Tainted ?, Tainted Forgotten, or Tainted Bethany.Sets Isaac's Red Heart containers to 1.