Keeper is able to pick up items independently from Isaac. He has his own inventory.
This inventory is not displayed on the HUD.
When Keeper dies, the items he obtained are permanently removed.
Keeper is not able to pick up any active items, trinkets, or consumables.
Keeper cannot pick up any type of hearts, except for Golden Hearts.
Eternal Hearts can also be picked up, but to no effect, effectively wasting them.
Keeper's speed is independent from Isaac's and does not sync like with Jacob and Esau. Obtaining speed items will grant speed only to the one that picked up the item.
Devil Room items will cost money instead of health as long as Keeper is alive.
When placing a bomb, Keeper will place another at no cost.
Keeper can be used to play Sacrifice Rooms at the cost of coins instead of hearts.
Keeper is not able to walk through doors or into Crawl Spaces, although he is able to enter the beam of light that takes Isaac to the next floor after the Mom's Heart/It Lives! fight, the one spawned by Genesis, as well as entering the big chest after defeating bosses in later stages.
Keeper is able to obtain items that grant extra lives and use them normally. If one of these items transforms the character into another character upon death, Keeper will respawn as that character and remain controllable.
The blue spiders will not spawn if the Keeper respawned with a respawn item.
Similar to Jacob and Esau, it is possible to take both items between item choice pedestals with careful positioning.
Even though Keeper is considered a second character, the run ends if Isaac dies.
Technically, Strawman is marked as a familiar item in the game's files, although most familiar-modifying items, such as BFFS! don't have any effect on Keeper.
Unlike Jacob and Esau, invincibility frames are not shared between Keeper and Isaac.
If collected in a challenge where Isaac is blindfolded, Keeper will be blindfolded too.
Re-emerging from the part of Mines II where Knife Piece 2 is hidden will cause Strawman to be regenerated from scratch. This permanently remove all items the summoned Keeper had collected up until that point.
If Strawman is picked up during the second lap of a Victory Lap, he will become The Lost alongside Isaac on every subsequent lap.
Crooked Penny / Diplopia: Picking up multiple copies of the item will spawn additional Keepers that each have their own inventory.
Genesis: Will not grant item choices for any of Keeper's collected items.
Tainted Cain: Items will not turn into pickups if Keeper takes them.
A "straw man" (sometimes written as strawman) is a form of argument and an informal fallacy of having the impression of refuting an argument, whereas the real subject of the argument was not addressed or refuted, but instead replaced with a false one. One who engages in this fallacy is said to be "attacking a straw man".
Picking up Strawman while having Money = Power or having it restored by exiting the Mother's Shadow sub-area causes the game to crash. If the order is reversed, the combination works normally.
If Keeper picks up Missing No., Strawman will not be removed from Isaac's inventory when Keeper dies and Keeper will not spawn spiders. Keeper will then respawn with no items upon picking up any familiar.