Obstacles

Obstacles are inanimate objects that are scattered around rooms, either trying to get in Isaac's way or benefitting him or his enemies.

Epiphany introduces 3 new Grid Objects into the game.

Twisted Rock

Twisted Rocks are special rocks decorated with a pentagram somewhere on it, having a chance to replace Tinted Rocks. Twisted Rocks have a large red pentagram surround them, which appears whenever an enemy enters its aura. Killing enemies within the pentagram will cause a spirit to fly into the rock, 'feeding' it. Destroying a Twisted Rock will cause it to drop pick-ups, and, if enough enemies are killed around it, can spawn the Dark Rock item.

The pick-ups that a Twisted Rock can drop include:

Sharp Rock

Sharp Rocks are pointy rocks that can be found exclusively in the first floor of Chapter 1 when playing as Tainted Cain, and they're part of Tarnished Cain's unlock process. Bombing a Sharp Rock will have it drop the Sharp Rock item, locking Tainted Cain into the unlock process.

Pillar

Pillars are Roman-style columns that can replace regular rock if the player has the Broken Pillar item, as well as found in the Philistine arena during the unlock process of Tarnished Samson.
The pillars can be destroyed by shooting tears at them and will drop boulders similar to Tarnished Samson's, that the player can pick up and throw. The boulders and the rock tears spewing from them follow the same mechanics as Tarnished Samson's ones, inheriting the player's tear effects.