Ok I found out why this works. But first the question of if it can be useful in a run, depends on the cards you have, how low you roll, and how many dice you have. This trick requires fury and Boomerang. To preform this trick all you have to do is pop fury, put a card in Boomerang, wait until it comes back to hit you (the first time), and then take the die out of Boomerang and boom, die replication. YOU WILL STILL GET HIT FOR THE FIRST PHASE OF BOOMERANG AND YOU HAVE TO PUT THE DIE INTO COMBAT ROLL FOR THIS EXPLOIT TO WORK CORRECTLY.

Also one thing I forgot to mention: You have to put a different die in combat roll during the Boomerang hitting the enemy animation

I know this glitch so I had on one speedrun

We need to find a way to do this without fury

I had this many times With the other glitches that the boomrang does not hit you back if you kill the monster

It's a glitch that don't occur on earlier patches and is totally useless. Yikes.

@Dking you didn't get a dice from the Boomerang back. It was a brand new dice created by applying Fury to Combat Roll. Fury triggered Combat Roll and not Boomerang because Boomerang takes much longer to complete its animation. Rewatch the video on x0.25.