If you're looking for the change from one item to another item sharing the same item slot, see Subtype change.
Transform is a mechanic by which an item or skill turns into another item or skill without losing enchantments and without losing its "used" identity in relation to Confiscate Evidence or its relation to Slavemaster's Knout/ICE-Bot/Activated Improbaglitchity Device/Gnome/Slingshot/Fair Trade (Class Talent)/The Space Stone/Sabotage. Also, items created by The Reality Stone or Race: Voidcaller will retain their "fade away" property after being transformed.
Transforming is confirmed to take place due to the following:
- Unstable Mutagen
- Evolution Stone
- Cronenberg World's Cronenberg virus
- Atom Bomb from The United Nations or The Lever changes Banana and Banana Peel.
- Radioactive Banana turns a Living item.
- RNGesus changes 2-25 random items.
- Wild Mode: What The Flux?! changes (up to) 25 random items.
- D6 changes (up to) 6 random items.
- Unidentified Loot Crate turns into an identified Loot Crate.
- Mystery Sprout turns into another plant item.
- Chikapu turns into Freakachu.
- Ugly Duckling matures.
- Core Crystal becomes a Magic Crystal.
- Peace Dove transforms a weapon into a peaceful item.
- Creeping Fungus transforms Red Mushroom into a Shroom Of Doom.
- Glitch transforms itself.
- Glitch Glock transforms another item.
- Glitchieke Doll transforms itself.
- Activated Improbaglitchity Device transforms another item(s).
- Interdimensional Fart transforms another item into a Lump Of Gold.
- D-Bug transforms another item.
- Skinning Knife transforms a (Captain's) Log.
- EnteredName The Platypus transforms into Secret Agent Platypus.
- Secret Agent Platypus transforms into EnteredName The Platypus.
- Bookworm transforms into Hungry Bookworm.
- Couscous transforms into Cous.
- Dino Egg/Dragon Egg/Golden Egg/Handegg/Inflatable Egg/Arcane Egg/Arctic Egg/Blazing Egg/Mecha Egg/Incubated Shapeshifter's Egg hatches.
- The Reality Stone (including in The Infinity Gauntlet) transforms another item.
- Caterpillar transforms into Cocoon.
- Cocoon transforms into a Butterfly.
- Purebread Cat/Sliced Bread transforms into Toast.
- Race: Arkly transforms a non-Jewelry item into a Jewelry item.
If Unstable Mutagen is used on a Horcrux, the transformed item retains the Horcrux enchantment, and Weakened Soul is not given. However, using Unstable Mutagen on Marieke Doll will trigger the passive to give out Wrath Of The Admin.
An item chosen (but not yet sent) with Raven does not retain its "chosen" status when transformed due to Unstable Mutagen. Unlike Raven, listed items in the intro paragraph above retain their relation. Evolution Stone relation needs testing.
If an item is transformed while visible in another inventory due to Sabotage, it can still be chosen successfully. The Smoking Mirror/Three-Eyed Raven relation needs testing.