The following article contains spoilers from Nightwing #93, on sale now.
The mystery of Heartless' origins have yet to be unveiled, but a crucial piece of the puzzle has been explained. One that raises the stakes for Nightwing, and anyone unfortunate enough to cross Heartless' path. Nightwing #93 (by Tom Taylor, Bruno Redondo, Wade von Grawbadger, Adriano Lucas, and Wes Abbott) revealed that Heartless has several mechanical body parts in place of organic matter, effectively making him an android.
This explains quite a number of things about him; his efficiency, the unnatural strength he exhibits for one man, and even how he was able to hide from members of the Bat-Family. However, this revelation also gives readers a perspective on what it will take to actually defeat him. Heartless took quite the beating in this week's issue, and what would easily have killed a normal human only slowed him down.
This issue raised a number of concerns about Heartless' full power. Up until now, it seemed like he was a serial killer with an above average level of training. Dangerous to be certain, but ultimately a problem Nightwing has come up against before. That all went out the window when Heartless managed to block a punch from Blockbuster with one hand. A normal human being would be incapable of that, but the how of it all was revealed after Blockbuster threw Heartless out of a skyscraper.
Heartless survived the fall, heavily injured, but alive and even conscious. He returned to his lair and his mysterious servant, Gerald. There, his servant, did a quick examination of him and revealed that most of his "enhancements" were intact, while looking at a screen of Heartless' body which indicated that only a few parts of him needed repairs.
This is a terrifying revelation. Aside from the horror of whatever Heartless did to himself to become this way, it also demonstrates just how durable his body is. The starting proof was his ability to block one of Blockbuster's punches, a character known for having super strength. The true proof of his threat level was proven when he walked away from a fall out of a skyscraper, a building tall enough to look over the skyline of Bludhaven. Even then, it only did a minor amount of damage.
It means that Nightwing probably won't be able to beat Heartless in a physical fight. Heartless is now on a different level, gaining physical enhancements that ensure he can survive even lethal force, something that Nightwing will never actually use. If he has any hope of preserving his dream for Bludhaven, then it may lie in Heartless' obsession. The one saving grace here is that Heartless' body doesn't appear to be entirely mechanical. Gerald's observations revealed that Heartless' body was mostly fine, but that his heart needed to be replaced. His servant walked over to the dozens of hearts his master had collected over the last few months, to select a replacement.
This confirms two things: The first, that Heartless does have some vulnerabilities. Second, that there is a purpose to stealing hearts beyond petty sadism. Gerald's familiarity with heart replacement implies that he's done this before. Perhaps this mechanical body is too much strain for the average human heart to handle over long periods of time. If so, then it makes sense that Heartless would steal hearts for his collection: he needs them to survive. His calling card however, might be the key to defeating him.