To unlock a transformation, you need to collect at least three items from a transformation set of items.

Fun Guy

Fun Guy

+1 Red Heart container.

Requires three of the following items :

Mega MushWavy Cap1up!Blue CapMagic MushroomMini MushOdd Mushroom (Large)Odd Mushroom (Thin)God's FleshMucormycosis
Adult

Adult

Grants a heart container.

Requires 3 puberty pills
Bookworm

Bookworm

Roughly 25% of the time, Isaac shoots an extra tear, like 20/20 item.

Requires three of the following items :

Anarchist CookbookBook of RevelationsBook of SecretsBook of ShadowsHow to JumpMonster ManualSatanic BibleTelepathy for DummiesThe BibleThe Book of BelialThe Book of SinThe NecronomiconBook of the DeadBook of VirtuesLemegeton
Spun

Spun

Gives +2 damage and +0.15 speed, and spawns a random pill upon transformation.

Requires three of the following items :

Experimental TreatmentGrowth HormonesRoid RageSpeed BallSynthoilThe VirusAdrenalineEuthanasia
Super Bum

Super Bum

Replaces Bum Friend, Dark Bum, and Key Bum for Super Bum. This bum collects any of the other beggars' pickups, and offers twice the rewards.

Requires three of the following items :

Bum FriendDark BumKey Bum
Bob

Bob

Isaac gains a green trail of poisonous creep.

Requires three of the following items :

Bob's Rotten HeadBob's BrainBob's CurseIpecac
Oh Crap

Oh Crap

Whenever a pile of poop is destroyed, health is replenished by half a heart.

Requires three of the following items :

Flush!The PoopBrown NuggetButt BombsE ColiSkatoleNo. 2Hallowed GroundDirty MindMontezuma's Revenge
Leviathan

Leviathan

Grants flight and gives +2 black hearts.

Requires three of the following items :

The NailSulfurAbaddonBrimstoneLord of the PitPentagramSpirit of the NightThe MarkThe PactMaw of the VoidEye of the OccultSanguine Bond
Guppy

Guppy

Grants flight and spawns a Blue Fly 50% of the time a tear hits an enemy.

Requires three of the following items :

Guppy's HeadGuppy's PawDead CatGuppy's CollarGuppy's Hair BallGuppy's TailGuppy's Eye

or trinket :

Kid's Drawing
Seraphim

Seraphim

Grants flight and gives +3 soul hearts.

Requires three of the following items :

The BibleCeltic CrossDead DoveGodheadGuardian AngelHoly GrailHoly MantleMitreRosarySacred HeartScapularThe HaloHoly LightSworn ProtectorDivine InterventionImmaculate HeartRevelationSacred OrbSalvation
Yes Mother?

Yes Mother?

Isaac gains a stationary knife that trails directly behind him. It synergizes like Mom's Knife would.

Requires three of the following items :

Mom's Bottle of PillsMom's BraMom's PadMom's BoxMom's ShovelMom's BraceletMom's Coin PurseMom's ContactsMom's EyeMom's EyeshadowMom's HeelsMom's KeyMom's KnifeMom's LipstickMom's PerfumeMom's PurseMom's UnderwearMom's WigMom's PearlsMom's Razor
Spider Baby

Spider Baby

Spawns a spider familiar that applies random status effects to enemies it comes in contact with.

Requires three of the following items :

Box of SpidersSpider ButtDaddy LonglegsHive MindInfestation 2Juicy SackMutant SpiderSissy LonglegsSpider BiteSpiderbabyBursting SackSpider ModSticky BombsParasitoidKeeper's KinThe Intruder
Beelzebub

Beelzebub

Grants flight and converts small enemy flies into Blue Flies.

Requires three of the following items :

Jar of FliesPlum Flute???'s Only FriendBBFBest BudBig FanDistant AdmirationForever AloneHalo of FliesHive MindInfestationSkatoleSmart FlyThe MulliganFriend ZoneLost FlyObsessed FanPapa FlyAngry FlyParasitoidYO LISTEN!Bot FlyFruity PlumPsy FlyThe Swarm
Conjoined

Conjoined

When attacking, the tumor faces shoot tears diagonally outwards, similar to the effect of The Wiz. Also gives -0.3 damage and slightly decreases tears.

Requires three of the following items :

AbelBrother BobbyDemon BabyDry BabyGhost BabyGuardian AngelHarlequin BabyHeadless BabyLil BrimstoneLittle StevenMongo BabyRainbow BabyRobo-BabyRobo-Baby 2.0Rotten BabySister MaggyFarting BabyFate's RewardIncubusMultidimensional BabySeraphimSworn ProtectorAcid BabyBuddy in a BoxKing BabyBoiled BabyCube BabyFreezer BabyLil AbaddonQuintsTwisted Pair
Stompy

Stompy

Upon getting three items or pills that increase Isaac's size, he will create dust clouds when walking and have a chance to spawn rock waves around him upon taking damage.

Requires three of the following items :

LeoMagic Mushroom and One Makes You Larger pill