|Guppy||Beelzebub||Super Bum||Yes Mother?||Bob||Fun Guy||Leviathan||Conjoined|
|Spun||Seraphim||Oh Crap||Bookworm||Spider Baby||Adult||Stompy|
Transformations alter Isaac's appearance and grant him special abilities.
A Transformation occurs when obtaining at least three collectibles from a particular set of items.
These collectibles always share a particular theme that corresponds with the transformation.
- Activated items (e.g. Guppy's Head) only need to be touched in order to count. Keeping them, or even activating them once, is not required.
- Rerolling items with a Dice Room, the D4, or the D100 will not remove progress towards the transformation.
- Transformations can be combined with each other, keeping the effects of any and all transformations with no effects overriding others.
- Transforming into Beelzebub for the first time will unlock the Lord of the Flies achievement.
- Since none of the Afterbirth transformations unlock an achievement or item, attaining them is not required for 100% completion of the game in terms of achievements.
- There are two transformations in the base game and nine more in the Afterbirth DLC.
- In the original The Binding of Isaac flash game, the transformation into Guppy was the only one available, making it chronologically the first.
- Rebirth introduced Beelzebub as the chronologically second transformation. It is so far the only transformation that unlocks an achievement.