Expansion Pack is an unlockable trinket in The Binding of Isaac, added in the Repentance DLC.

When Isaac uses an active item, the effects of another random active item are activated in addition to the original item.

Can only grant active items that have a charge time of 1 or 2 rooms.

Timed recharge and infinite use items will trigger the effect only once per room.

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 Isaac, ???, Satan, and The Lamb as Tainted Bethany.

The following special synergies and interactions for Expansion Pack 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.

Expansion Pack

• (without c-439): When an active item is used, also uses the effect of another random 1- or 2-charge active item
• Golden Trinket (without Mom's Box): When an active item is used, also uses the effect of 2 random 1- or 2-charge active items
• Mom's Box: When an active item is used, also uses the effect of 2 random 1- or 2-charge active items
• Mom's Box + Golden Trinket: When an active item is used, also uses the effect of 2 random 1- or 2-charge active items and a random 3-charge active item

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