Bosses such as Chub or Carrion Queen can swallow the decoy bomb just like a regular bomb.
Isaac can push the decoy bomb by walking into it or shooting it with his tears just like regular bombs.
If Isaac leaves and re-enters a room after placing the decoy bomb, its explosion timer will be set to that of a regular bomb (1.5 seconds).
Synergies
Book of Virtues: Creates wisps that are small Isaac heads with a white flame in the middle ring. Tears shot by these have a 7.5% of applying the mark status effect, akin to Rotten Tomato.
Car Battery: Spawns two decoys on top of each other.
Edmund McMillen stated that Best Friend would no longer "Die upon touch". This is a reference to a bug in the original The Binding of Isaac where, in many circumstances, Isaac could take glitched hits (often killing Isaac outright).
Best Friend works remarkably similar to Pipe Bombs in Left 4 Dead, down to the 5 second timer and not working on bosses.
Gallery
The icon of Best Friend as seen on the lower 3DS screen.
Mega Troll Bomb.
Bomb modifier items will affect Best Friend, with the exception of 
Bobby-Bomb, 
Bomber Boy, 
Fast Bombs, 
Mr. Mega, and 
Rocket in a Jar.
Scatter Bombs will create mini decoys.
Chub or 
Carrion Queen can swallow the decoy bomb just like a regular bomb.
Book of Virtues: Creates wisps that are small Isaac heads with a white flame in the middle ring. Tears shot by these have a 7.5% of applying the mark status effect, akin to 
Rotten Tomato.
Car Battery: Spawns two decoys on top of each other.
Remote Detonator + 
Schoolbag: The decoy bomb is affected by remote detonator.
Bug!
The Binding of Isaac: Rebirth
