Antibirth adds several new objects and obstacles to help or hinder Isaac's progress.
Walking up to the machine and bumping into it will cost one penny. In exchange, the machine has a chance to recharge 1 to 3 charges of Isaac's currently held active item. It also has a chance to do nothing or harmlessly shock Isaac. The harmless shock has the same effects as Voodoo Pin, and will ignore Holy Mantle.
The machine is also able to add an extra two levels of charge to active items, similar to the Battery, with one extra level.
If destroyed, it drops several pickups.
It has a small chance to instantly kill Isaac, regardless of health. What exactly triggers this is still unknown.
Buckets have a chance to spawn the following when destroyed:
Spiked rocks behave like regular rocks, but damage Isaac upon contact. They cannot be flown over.
Red TNT barrels explode when destroyed. Unlike regular TNT barrels, red TNT only needs to be shot once to be detonated.
They also detonate if Isaac or an enemy walks into it.
Tall blocks are indestructible and impede movement, even if Isaac has flight.
If Isaac is under Mega Mush's effect, he can crush tall and regular metal blocks.
Teleporters appear in the Mausoleum. Stepping on one teleport pad transports Isaac to a different, matching pad.
Red Bombs are special bombs found in the Mines. They can be picked up and thrown, and will detonate after a short time even if still held. They cannot be carried between rooms.
Antibirth adds many new functions to buttons. In some rooms, buttons can destroy certain rocks, create bridges across gaps, or spawn enemies.
A few rooms have red buttons which kill an enemy in the room, usually when it's unreachable by Isaac's tears.
Minecarts ride along rails in the Mines, carrying enemies, Grimaces and sometimes even fires along a fixed path. Minecarts are destroyed when the enemies inside are destroyed. If the Minecart was carrying a fireplace, the minecart will not be destroyed when the fire is put out.