'M is an unlockable trinket in The Binding of Isaac, added in the Repentance DLC.

Rerolls Isaac's active item every time it's used.

The rerolled active item will start with no charges.

Transformations will not be given from active items acquired via this trinket, even if the item was dropped and picked back up again.

Active items that have costs associated with using them (e.g. coins for Magic Fingers), will still be rerolled even if they cannot be used.

The active item's charge must be fully expended in order for it to reroll.

One-time-use items will disappear before being rerolled.

This page shows the latest information as of the new Repentance+ (Online Co-op) DLC.
To see information about this trinket for the previous Repentance version, check this page instead.

Defeat Mother as Eden.

The following special synergies and interactions for 'M have been documented.

* Note that not all possible synergies and interactions are listed here.

Below is the Internal Item Description as shown in-game.
Note that some stat changes are not displayed here. Please see the main description for the full effects.

'M

• Rerolls Isaac's active item each time it is used
• Golden Trinket (without Mom's Box): 10% chance that the rerolled item will be fully charged
• Mom's Box: 10% chance that the rerolled item will be fully charged
• Mom's Box + Golden Trinket: 20% chance that the rerolled item will be fully charged

• Check out the trinket description on the external Isaac Wiki.