[GAMEPLAY] I figured it out! Inflicting Grievous Wounds allows you to kill Target Dummies
I saw someone else's post on here where he mentioned Taliyah was able to kill Target Dummies through a certain method. I tried it myself, but couldn't get it to work. I then started messing around and found that Kayn was able to kill Target Dummies. I wasn't sure why this was, so I decided to see if it was item related, so I sold all of my items as Kayn and tried to kill a dummy. It didn't work. So then I tested out each item I had purchased individually, and found that I could only kill Target Dummies while I had a Mortal Reminder equipped.
Then I tested to see if it would work with just an Executioner's Calling, and I could kill dummies still. Pretty certain I figured it out, I then tested out several other methods of applying Grievous Wounds, such as Morellonomicon, Ignite, and Varus' Volley of Arrows. I was unable to kill dummies until I applied Grievous Wounds (In Morellonomicon's case, I bought 6 Deathcaps, and was unsuccessful, but then I sold 1 to buy a Morellonomicon, and it worked).
I know this has been a relatively well-known bug recently, so I hope this helps :)
P.s. I'll bet that guy who killed dummies with Taliyah had a Morellonomicon equipped.