The most recent example would have to be Hawkeye’s deadly arrow from Civil War II. That arrow hit its mark and, to its credit, it did kill Bruce Banner before he was able to transform. For a little while, at least. That’s likely because the arrow was created by the only man in the world who knew the Hulk and his physiology well enough to create such an effective projectile: Bruce Banner himself. Unfortunately, that killing blow came with consequences, chief among them being the Immortal Hulk and a newly-ostracized Bruce Banner who is on the run in Al Ewing’s Immortal Hulk #1. The story solidifies Hulk’s new immortal status, which is cause to wonder if Hulk-Smiter would stand a chance against the seemingly unkillable creature.
Look deep enough into Marvel Comics canon and you’ll find evidence of a mechanical being called the Hulk-Killer, a synthetic humanoid created by the Leader and later reactivated by General Thunderbolt Ross, Hulk’s long-time nemesis, to fulfill its titular purpose. In classic fashion, the Hulk-Killer might have completed its task if it weren’t for the great Achille’s Heel of villain-built weaponry from the 1960’s -- faulty wiring. It’s believed that the Hulk-Killer was, in fact, powerful enough to kill any Hulk, but maybe only after a reboot or two. This is Silver Age Hulk, though, so it might be unreasonable to assume that the same rules apply to 2018’s Hulk. It certainly would seem reasonable for the Immortal Hulk to tear through a puny robot these days, huh?
Then there’s the most famous Hulk deterrent of them all, Tony Stark’s Hulkbuster Armor, a mechanical suit designed to be deadly enough to take on the Hulk should the hero go on a rage-fueled rampage. The armor was popular enough to make its way into the Marvel Cinematic Universe for Avengers: Age of Ultron and has seen numerous iterations throughout the comics. In most cases, the armor is enough to beat down the Hulk but not outright kill him, which doesn’t seem to be its purpose anyway.
Whether Hulk-Smiter turns out to be the tool Thor will eventually need to score the killing blow on the Immortal Hulk, or if it’s just another hammer on the road to reforging Mjolnir, remains to be seen. Regardless, if the hammer is able to down the Hulk permanently then it may go down in history as Mjolnir’s better. Decide for yourself in Thor #1, available in comic books stores now.