Introduction
The Binding of Isaac: Rebirth (and its expansions Afterbirth, Afterbirth+, and Repentance) is a top-down dungeon-crawler roguelike with an item pool so massive you'll still find new combos after 1,000 hours. Every run is different because item synergies can completely redefine how you play. At its core, the game is about damage, tears, and survivability — but the interactions between hundreds of items create emergent gameplay that few other roguelikes can match.
This guide covers Repentance's complete mechanics. If you're playing on the original Rebirth or Afterbirth+, most of this still applies, but some items and paths (notably the alt-path floors, Tainted characters, and Mother's boss fight) are Repentance-exclusive. Let's break down what makes Isaac tick, starting with the items themselves.
Item Types & Tiers
Items fall into several categories, and understanding which ones to prioritize is the difference between dying on Basement II and rolling through the Chest.
Passive Items (S-Tier must-grabs):
- Sacred Heart: +2.3 damage up, homing tears, 1.5x damage multiplier. The single best item in the game. It's an Angel Room exclusive with an incredibly low weight — if you see it, your run is won.
- Incubus (Succubus): Grants a demon familiar that fires your tears alongside you. Effectively doubles your DPS. Succubus also gives a damage aura. Both are top-tier.
- Brimstone: Charged laser beam. Infinite piercing, high damage. Combos with almost everything. With Tammy's Head, you fire 10 brimstone lasers at once — an instant room-clear.
- Godhead: Homing tears with a damaging aura. Requires an Angel Room after unlocking it. The aura damage scales with your damage stat, so even if your tears are weak, Godhead's aura carries hard.
- Magic Mushroom: +0.3 damage, +0.3 speed, +1 HP, 1.5x damage multiplier. The best "simple" item in the game. It's common enough that you see it regularly, and it single-handedly carries the early game.
Active Items (S-Tier):
- Book of Revelations: Every use gives a Soul Heart and increases the chance to fight Death (the easiest Horseman). Guarantees a Devil Room on the floor you use it. The sustain alone makes this S-tier.
- Mega Mushroom: Full screen clear, invincibility, massive damage for the current room. 4-room charge. It's effectively "win this room" every 4 rooms.
- D6 (Isaac's starting active): Rerolls items. The most versatile active in the game and the reason Isaac is the best character for learning item mechanics.
- Spindown Dice: Converts items into other items at a fixed offset. You can "downgrade" Breakfast into Sacred Heart if you know the 1,000+ item ID list. Requires external knowledge, but the power ceiling is absurd.
Tear Modifiers (build-defining):
- Mom's Knife: Replaces tears with a piercing knife. High damage, charges for a throw. Combos poorly with Brimstone but synergizes with piercing items.
- Technology: Replaces tears with a continuous laser. +0.2 damage every time you take a damage upgrade. Without synergies, it's decent but falls off late-game.
- Ludovico Technique: A single controllable tear that floats around the room. Incredible with damage-over-time effects (Ghost Pepper, Tech X) but miserable with low tear rate. Proceed with caution.
Devil Rooms vs Angel Rooms
One of the most important strategic decisions in Isaac is whether to take Devil Rooms or Angel Rooms. Devil Rooms appear after a boss if you haven't taken red-heart damage on that floor. Opening a Devil Room door costs 1-3 Heart Containers (depending on the items inside). Angel Rooms replace Devil Rooms if you refuse the Devil deal or if you have certain items (Rosary, Eucharist, etc.).
When to take Devil Rooms:
- You have enough health to spare. If you're on 3 red hearts, a 2-heart Brimstone deal could kill you if you get hit in the next floor.
- The item is S-tier. Brimstone, Mom's Knife, Abaddon, Ceremonial Robes, or Dark Bum are worth the HP cost.
- You have a way to generate health (Guzzling D4, Satanic Bible, or a Greed's Gullet + coins setup).
When to skip to Angel Rooms:
- You're going for the Mega Satan path (requires 2 Angel Room key pieces) or the Mother path (which doesn't benefit from Devil Rooms as much).
- You're playing The Lost or Tainted Lost — they can't take red-heart damage for Devil Rooms anyway, and Angel Room items (Sacred Heart, Godhead, Crown of Light) are safer and stronger.
- Your health is too low to afford any Devil deal. Sometimes a Spirit Heart in the Angel Room is more valuable than a Devil item you can't afford.
Devil Room item tier list (take these every time): Brimstone, Mom's Knife, Abaddon (Satanic Bible on non-Blue Baby characters), Ceremonial Robes, Dark Bum, Lil' Brimstone, Maw of the Void. Skip: Brother Bobby, Sister Maggy, Demon Baby, Binky.
Character Unlocks & Tips
Isaac: The starting character. His D6 makes him the best for learning and for breaking runs. Play Isaac until you've filled the item collection page — it teaches you the entire mechanic set.
Cain: Unlocked by holding 55+ coins in a run. Starts with a Lucky Foot (better room drops, guaranteed pill identification) and +1 speed. He's a consistent early-game character. The Foot also prevents "bad" pill effects — you can freely use any pill.
Judas: Unlocked by beating Mom's Heart 2 times. Starts with The Book of Belial (1-room charge, +2 damage for the room). High damage, low health (1 red heart). Judas rewards aggressive play — use Book of Belial in every room, especially boss rooms.
Azazel: Unlocked by beating Satan 3 times. Short-range Brimstone, flight, and 3 black hearts. He's the "easy mode" character — but his short range teaches bad habits. Use Azazel to unlock The Forgotten (beat the first floor in under 2 minutes to get the Broken Shovel).
The Lost: Unlocked by dying in a Sacrifice Room with a Missing Poster trinket. Starts with flight, spectral tears, and Holy Mantle (one free hit per room). No health at all — one hit removes Holy Mantle, the next kills you. The Lost is a test of patience. Angel Rooms are your best friend. Take every Curse Room since you can fly over spikes for free items.
Forgotten: Unlocked via the Broken Shovel puzzle. He wields a bone club (melee) and a soul (floating ghost). The melee ignores shields and rocks, making early-game rooms easy. The soul uses the active item. He's complex but incredibly powerful once you learn to alternate between the two forms.
Tainted Characters (Repentance): Unlocked by using the Red Key, Cracked Key, or Soul of Cain in Home (the floor after the Chest/Dark Room). Each Tainted character fundamentally changes the game. Tainted Isaac is limited to 8 items, but the items are randomized from the entire pool. Tainted Lost has Holy Card (one free hit per floor instead of per room) but no defensive items. Tainted Forgotten has a giant skeleton that throws its head — one of the highest damage potentials in the game.
Boss Patterns & Strategies
Mom / Mom's Heart (early game): Mom stomps, spawns enemies, and shoots tears. Stand on the side opposite her foot. When she stomps, move diagonally. Her foot is vulnerable briefly. Mom's Heart fires tear bursts in a cross pattern. Stay near the door and weave between the tear lines.
Satan (Sheol): Phase 1: Satan slams his claws down. Stand between them for damage-free windows. Phase 2: He spawns a ring of fire and attacks with a laser. The laser's direction is telegraphed — stand perpendicular. Phase 3: Satan's head detaches and shoots brimstone lasers. Stay near the top of the room to dodge sideways.
Isaac (Cathedral): Phase 1: Isaac shoots homing tears and spawns angelic beams. The beams are telegraphed by a cross shape on the floor. Phase 2: Isaac's body is replaced by an angelic statue that shoots Brimstone lasers. The lasers aim at your position — move perpendicular as they fire. The key: Isaac's HP is low compared to other final bosses. If your DPS is high enough, you can skip Phase 2 entirely.
??? / Blue Baby (Chest): Fires brimstone beams in a rotating pattern. His bloodshot eyes track you and fire. The key mechanic: every few seconds, Blue Baby spawns a puddle of creep that damages you on contact. Don't stay in one spot for more than a second. Keep moving in large circles around the room.
Hush (Blue Womb): The toughest early-game boss. 3,000 HP with armor (damage cap of ~100 per hit). Phase 1: tear burst patterns, continuum tears (they wrap around the screen), and spawning enemy clusters. Phase 2: brimstone lasers and continuum brimstone rings. Hush's main gimmick: he stops taking damage briefly to spawn enemies. Use this time to reposition. The fight is a marathon — prioritize dodging over DPS. With 3+ damage and enough sustain, you can outlast him.
Delirium (Void): Teleports randomly, morphs into other bosses, and has no consistent attack pattern. Delirium's room also damages you on contact (the edges of the room are hazard). The fight is pure chaos. Maximize DPS and accept that you'll get hit. Homing tears are invaluable here since Delirium teleports constantly.
Mother (Repentance — Corpse): A complex multi-phase fight. Phase 1: claw slams and shockwaves. Phase 2: Mom's Hands grab at you while Mother fires brimstone. Phase 3: The ground breaks and you fall into a smaller arena. Mother fires a massive continuum brimstone laser. The key is learning the claw telegraph — the shadow appears before the slam. Dodge sideways, never backward.
Alternate Paths & Endings
Repentance added alternate floor paths that branch from the Downpour (instead of Basement) through the Dross, Mines, Ashpit, Mausoleum, and Gehenna before reaching the Corpse. These paths are harder than the standard route but offer better rewards and unique bosses.
- Downpour/Dross: Accessed by interacting with a bookshelf in Basement/Burning Basement. The mirror world in Downpour II has a cracked tinted rock holding a Knife Piece (needed for Mother).
- Mines/Ashpit: Accessed from Caves/Flooded Caves. Minecart mechanics let you cross gaps or access secret rooms. Second Knife Piece is here.
- Mausoleum/Gehenna: Accessed from Depths. Double-key rooms contain unique items. The boss here drops the Lump of Coal or the Mausoleum-specific transformation items.
- Corpse: The end of the alt path. Home stretch after assembling the Knife. Mother awaits.
Endings by path: Mom's Heart → ??? is the standard win (Credits). Cathedral → Isaac → Chest → ??? unlocks Polaroid invincibility. Sheol → Satan → Dark Room → ??? unlocks Negative damage. Void → Delirium is the "epilogue" boss. Corpse → Mother unlocks additional endings for each character. The Beast (Home) requires using the Red Key in the starting room and offers the most dramatic finale — four-phase boss fight that's arguably the hardest but most rewarding in the game.
Transformations & Synergies
Collecting 3 items from a set triggers a transformation that grants permanent stat boosts. Some transformations are build-defining; others are nice-to-have bonuses.
- Guppy: 3 Guppy items. Spawns blue flies on every hit. The most iconic and strongest transformation. Guppy's Head (active, spawns 20 flies), Guppy's Collar (revive chance), Guppy's Paw (convert red hearts to soul hearts), and Dead Cat (9 lives) are all excellent items individually. Actively fish for Guppy by using Red Chests and Curse Rooms.
- Leviathan: 3 Devil items. Grants flight and a fear aura. Easy to achieve if you're taking Devil deals. Not as strong as Guppy, but flight is always valuable.
- Seraphim: 3 Angel items. Grants flight and a damaging aura. If you've been going Angel Rooms, you'll naturally trigger this by the end of the run.
- Mom: 3 Mom items. +1 speed, +1 tear rate. Mom items (Lipstick, Pad, Underwear, etc.) are generally weak, but getting Mom's Knife triggers the transformation alongside two others.
- Spun: 3 syringe items. +0.2 speed, +0.7 tear rate. Speed Up pills and Growth Hormones count. A solid combat transformation.
- Beelzebub: 3 fly items (Ghost Pepper, Skatole, Hive Mind, etc.). Gives flight and a poison trail. Situational but powerful if you're building a fly-focused orbital defense setup.
Greedier Mode
Greedier Mode is a wave-based survival gauntlet with a fixed shop between rounds. You fight 10+ waves per floor, then a boss, then the final Greed fight. The key differences from normal mode:
- Ultras are harder: Greedier's Ultra Greed has a damage cap, faster attack speed, and more HP. His coin attack spreads wider.
- Donate wisely: The Greed Donation Machine appears after the boss. Donate 1 coin at a time — the machine jams frequently. If you donate too fast, half your coins get wasted. Donating 879 coins total unlocks the Keeper character (and 1,000 coins unlocks his upgrades).
- Character choice matters: Azazel and Lilith dominate Greedier Mode. Azazel's short-range Brimstone clears waves instantly. Lilith's Box of Friends doubles familiars, creating an army by the third floor. D20 break runs are possible — use the D20 to reroll pickups, creating chests from coins, which drop more items. With enough patience, you can fill the entire floor with items.
- Shop strategy: Buy every battery you see for active item spam. Restock Box (shop item) lets you buy unlimited items from the shop. If you find Restock + Blank Card + Jera rune, you win the game immediately — duplicate batteries infinitely and buy everything.