Bucky Barnes, Cap's replacement, showed up out of nowhere in Fear Itself only to be manhandled by the new Red Skull. She slaps him around with his own severed bionic arm before being impaled by a magic hammer.
Turns out he was still alive. He was severely injured, but we find out that Bucky's death was faked to get Steve Rogers back in the Captain America costume and lead the others that way.
Played straight with Jack Monroe (the former 50's Bucky and later the costumed Anti-Hero Nomad). After wallowing in Comic-Book Limbo for years, he showed up for a few pages in Ed Brubaker's Captain America run just to be shot and killed by the Winter Soldier. The same fate befell the Red Skull's former lover, Mother Night.
Though Monroe at least later got to be the subject of A Day in the Limelight issue focusing on the days leading up to his murder.
After the House of M event in the Marvel Universe, many mutants lost their powers. The ones who got it the worse were probably a set of young student X-Men, mostly minor characters in the series, who were literally Put on a Bus... then the bus was hit by a missile. Every one of them died.
Exiles member Sunfire was killed off by dropping a literal bridge on her. Or maybe it was a building. I can't remember because it happened off-panel.
Jean Grey's death in the 2003 "Planet X" storyline fits this to a "T". Her marriage to Scott had a bridge dropped on it in more ways than one at the same time.
Furthermore in Ultimate Spider-Man, Gwen Stacy does what she does best: dying. But whereas her death in the classic continuity was a major series turning point and one of the most shocking and unexpected events in the history of comics, forever solidifying Norman Osborn as Peter's greatest nemesis, in the Ultimate universe she's jumped in Peter's backyard by mindless monster Carnage and sucked dry. The suddenness and brutality of her Ultimate death still caused it to have a considerable impact on the series though and in any case she comes back. As Carnage!
Crisis Crossover series, especially at DC, are notorious for killing off characters who've been around a long time in awkward, Red Shirt like ways, just to show how bad the Big Bad is. These characters are lucky if they get more than one or two lines of dialogue. Some examples include the Losers, Dove of Hawk and Dove, and the original Mirror Master in Crisis on Infinite Earths, Justice Society of America members Atom (Al Pratt) and Dr. Mid-Nite in Zero Hour (Hourman also died, but he got better), and most of the Freedom Fighters (Phantom Lady, Human Bomb, Black Condor) in Infinite Crisis.
Teen Titans characters like Pantha and Wildebeest died just to give Superboy-Prime, who'd already had a Face–Heel Turn, a moment where he crosses the Moral Event Horizon. Neither of these characters are given many lines, or a chance for those not familiar with them already to get to know them, before they die.
In the ninth chapter of Crisis on Infinite Earths, Brainiac and the Silver-Age Lex Luthor lead an army of villains. Golden-Age Luthor (who'd been around since at least the early 1940s) appears just long enough to say that he, not Silver-Age Luthor, should be their leader. Brainiac says "You are right. We do not need two Luthors.", and disintegrates Golden-Age Luthor. No final battles with Superman for that Luthor. Instead, he goes out like your usual faceless henchman.
Countdown to Final Crisis has several, though the most egregious examples of victims to this fate are Duela Dent, the Jokester, Trickster, and three entire Earths. Countdown is very mean spirited overall.
There's a good amount of this in Blackest Night, often to make room for their replacements/predecessors. Tempest gets his heart ripped out by Black Lantern Tula, making room for the Young Justice version of Aqualad, and the second Hawk is also killed to free up space for her predecessor to return. Dr. Polaris gets it bad too, dying off-screen. Captain Boomerang Jr. went from being an antihero who had movie nights with Supergirl to someone who helps his Obviously Evil zombie father kill and devour women and children. Firestorm's girlfriend Gehenna got her heart ripped out and turned to salt simultaneously.
After countless times of escaping death, after being one of the most evil and powerful of supervillains, after clashing with Superman and the Green Lantern Corps and allying himself with the some of the greatest evil powers of the DC universe (Mongul and the Anti-Monitor being a few), how does the normally unkillable Hank Henshaw finally die? He makes the mistake of transferring into a cybernetic character who already has a soul, and then is soul-killed by said character which Word of Godsays is permanent. What makes it worse is that he is killed by a supporting Green Lantern character who has only made less than a dozen appearances total, and while on the astral plane he was just an ordinary human; reflective of his soul. So his end was in a crubstomp fight of a trained warrior woman killing an elderly man. And, as it turns out, Death Is Cheap, so the situation's not quite so bad as it seemed. Or worse, since Henshaw wants to die.
Marvel's Ultimatum is infamous for this trope, as it kills off over half the cast of Marvel's Ultimate Universe in brutal, violent, pointless ways similiar to many of the above DC examples. The most infamous is the Blob's gruesome murder of the Wasp.
Same thing happened to The Vision from Young Avengers during the above-mentioned Children's Crusade. He got unceremoniously destroyed in the final issue (and his friends refused to even TRY and rebuild him), right around the time Brian Bendis decided to bring back the original Vision.
Rick Remender created Father and the Descendants in his Uncanny X-Force run, and later had them appear as major villains in the final arc of Secret Avengers. Despite building them up in such a big way, he casually killed them off near the beginning of Rage of Ultron to show that Hank Pym had crossed the Moral Event Horizon.
Due to Executive Meddling, this was the fate of all of the Dead Universe Transformers in Simon Furman's Transformers comics for IDW. Grindcore, Straxus, Cyclonus, Bludgeon, Thunderwing, and Monstructor were all destroyed (or presumed to be destroyed/deactivated) offscreen after the Autobots managed to deactivate the machines keeping them from disintegrating in the Live Universe. While this was probably going to be the case anyway, it felt like a Bridge Dropping because these characters had all of four issues to terrorize the Autobots, and it was left unclear whether the mind-controlled Decepticons died or were defeated offscreen.
Later stories revealed that Cyclonus, Bludgeon and Monstructor all survived, but confirmed the deaths of Grindcore and Straxus. Thunderwing's still up in the air, though Furman suggested that if he didn't reappear, the Autobots threw him into the nearest black hole.
A few years ago, Harbinger, one of the heroes of Crisis on Infinite Earths, was abruptly killed offscreen by Apokolips forces in the pages of The Supergirl from Krypton when she tried to prevent them from kidnapping Supergirl from Themiscyra, a role that could have easily been filled by any generic Amazon. Can't anybody from that story get a happy ending?
This happened to Ryan Choi, the second Atom in the pages of DC's Titans: Villains For Hire at the hands of Deathstroke to make Slade seem like more of a threat. The fact that this is the second Asian character to get killed by DC to make a villain seem more dangerous in as many months (the first being Lian Harper) has not gone over well with fans.
Especially since A) this was Deathstroke who's already been established as one of the most ruthless badasses in the DCU for over twenty years and B) the person who hired him turned out to be Dwarfstar, a character who was created specifically as Ryan's nemesis.
The reception was so poor that the entire series of events was retconned in The New 52 and now Ryan is back to being alive. An additional Author's Saving Throw was implemented in Convergence, where it was revealed that Ryan's consciousness had survived after his body's death.
Terra 2 from Teen Titans gets pointlessly killed one day to make way for a Legacy Character, in the form of her sister. She didn't even live long enough to even reunite with said sister, let alone having her true origin revealed to her: she was a princess from a underground kingdom who was given human form (of Terra, oblivious of the fact that Terra was evil), who was ultimately kidnapped by the Time Trapper and mindfucked into thinking she was from the year 2001 as part of an underground group of rebels fighting against the mad son of Donna Troy.
All the way back in 1942, Fiction House's Rangers Comics changed its focus from supehero stories to more down-to-earth stories involving American soldiers. The Rangers of Freedom, the super-hero team, became ordinary army rangers. Most of them got bayoneted off-panel before the story ended.
A villain example occurred in the Spider-Man miniseries, The Hobgoblin Lives. Jason Macendale, the second Hobgoblin and major villain for nearly two decades, was quickly shot and killed in one page in order to make way for the original Hobgoblin to return. Given his Villain Decay it was probably for the best, as he'd been revamped twice as Demogoblin and as a cyborg. Ironically, this occurred in a miniseries that reversed a previous bridge drop on the first Hobgoblin. Longtime supporting Spider-Man character, Ned Leeds had been unceremoniously killed by assasins in a Spider-Man/Wolverine miniseries. As Roger Stern, the creator of the original Hobgoblin had left Marvel Comics before he could reveal who the Hobgoblin really was, the Editorial staff decided that Leeds would fit the bill. Despite the original Hobgoblin having taken the Goblin formula making him powerful enough to avoid his death or at least survive it. Stern took the opportunity years later to fix the issue and establish his original choice Roderick Kingsley as the true Hobgoblin. By that logic Macendale had to go.
Toxin (or more specifically his host, Patrick Mulligan) was unceremoniously murdered offscreen by Blackheart and the Toxin symbiote was confiscated, only to later be forced onto Eddie Brock by Crime Master.
Likewise, his fellow symbiote hosts Hybrid and Scream were later killed by Eddie Brock. This is made more egregiously humiliating by the fact that Brock was completely without powers at the time, and not even his own prior symbiote experience should have been enough with the way things went down. Combine that with the reality that neither Donna nor Scott were amateurs, and that Scott/Hybrid had the power of 4 symbiotes in one, made for a tragic end to both characters.
Banshee was regarded as dying like this when Vulcan crushed him with the Blackbird, as were several mutants killed after House of M. The fanbase is not pleased that at least one major character is killed each story.
Nightwatch was a character who actually had his own comic book; when sales of said book tanked, he was killed rather unceremoniously by an armored criminal named F.A.C.A.D.E. (Who also killed Lance Bannon; the killer's identity remains unsolved, as it was eclipsed by The Clone Saga, but it was never officially aborted.
Dr. Octopus died during The Clone Saga. His death happened thusly: He's sitting in a police car. And then Kaine comes and kills him. And then Kaine jumps away.
The same thing happened to the Grim Hunter, one of Kraven's sons. (These attacks by Kaine for no known reason would eventually be explained later.)
Spider-Verse infamously did this to a bunch of Spider-Men. Particularly the ones from the cartoons, who got off-panel panel deaths. Made worse by the fact that they hadn't been used in over a decade, so they were called out of retirement for the express purpose of serving as cannon fodder.
This happens to Ethan Rayne in the comic adaptation of Buffy the Vampire Slayer. He's shot by the bad guys while imprisoned, prompting him to disappear from a dream sequence he's helping Buffy with. She walks into his cell, taunting him, only to find him dead.
The sad story of heroine Mystek ended with this. Created by Christopher Priest and was intended to be have her own mini-series, DC Comics asked Priest to insert her into Justice League Task Force to churn up interest. However, DC decided to turn down the idea of the mini-series, leaving Priest with a most-likely unwanted character. So, he promptly makes her claustrophobic, panics and ends up getting shot out of an airlock in her panic.
The Sonic the Hedgehog comic did this to almost the entire echidna population with everyone except for Knuckles and Dr. Finetivus are trapped and apparently wiped out within the Doctor's Warp Ring.
Not that Finetivus escaped this trope. At the end of the "Worlds Collide" crossover, Finetivus, along pretty much every single supporting character the comic had, was wiped from existence completely.
Transformers: Wings of Honor: While most deaths got some dramatic tone to them (Dion and Magnum got The Hero Dies, and Metalhawk's death marked the point of no return for Onslaught), Over-Run got his helicopter dropped on top of him and Ironfist (while Ironfist survived, Over-Run didn't). The Stealth team also got hit with this. After an entire narrative focusing on their adventures, they come to base and get caught right up in the climax, Powerflash dying offscreen, and Tap-Out's corpse being seen once the battle was over. A deft shot later kills Rumbler in the second arc.
In the Runaways arc "Home Schooling", someone fired a missle at the Runaways' home, killing Old Lace and triggering a violent episode from Klara. Later, Old Lace's partner Chase gets hit by a car. Apparently, the story arc was supposed to end with the resurrection of Gertrude Yorkes, but it would seem someone at Marvel was displeased with the increasingly dark tone of the arc, so the whole series was put on a hiatus, and the events were later minimized.
Kid Eternity had just joined the Teen Titans during Sean McKeever's run, but was quickly and unceremoniously written out in a following arc by Bryan Q.Miller. Eternity was kidnapped by the Calculator, as apparently it was felt by editorial that he was too "overpowered" of a character and would interfere with the Blackest Night event. His status remained vague and up in the air until it was later revealed that the Calculator had tortured him into constantly summoning his dead son's spirit, and then when his powers burnt out, brutally beat him to death. To make the death even more ridiculous, the Titans would not express any concern for their teammate or remember his existence until a much later arc in JT Krul's run, where the Calculator reveals Eternity's death to them.
G.I. Joe (IDW) did this to the entirety of the Ninja Force (generally considered an embarrassment from the Dork Age of the toy line and the unfortunate final days of G.I. Joe: A Real American Hero (Marvel), albeit, not enough so to make this an excusable act); having them brutally murdered during the 'Cobra Civil War' arc as part of a competition by contenders for the Cobra Commander position to see who could kill the most Joes.
The Transformers: Last Stand of the Wreckers: Many of the deaths were intentionally written as this as a Deconstruction of the franchise's glorified portrayal of war. Rotorstorm is unceremoniously shot just as they arrive, Pyro attempts a Heroic Sacrifice but only ends up getting ripped to shreds without getting a shot off, and Ironfist dies of unrelated injuries after the action settles down. Kickoff gets torn apart offscreen. The death given the most ceremony is Topspin and Twin Twist as Topspin heroically sacrifices himself to stop Twin Twists torture and both go out with a battle cry. As Pyro points out the death was to turn on a computer. On the bad guys side, Wingblazer and Skyquake get shot by Overlord because he was annoyed.
Narrowly subverted in The Transformers: Robots in Disguise. During the Decepticon attack on New Iacon in the last arc of season 1, Broadside is seemingly crushed to death at random when Devastator caves Autobot Command in with him still inside. For quite a while most fans assumed that this was his fate, but issue 29 of More Than Meets The Eye reveals that he survived and joined up with the Lost Light crew.
In Robotech: Prelude To Shadow Chronicles, Breetai is killed along with the Regent when General Edwards fires on the Regent's flagship. And this was in the middle of Breetai's duel with the Regent. Therefore, Breetai is killed by what is technically supposed to be still friendly fire at this point, but then again, Edwards is already known for his general dislike of non-humans. Exedore is killed aboard the Deukalion (confirmed in the animated followup). The Neutron-S missiles are not what they seem to be and Exedore chooses the wrong moment (when it's too late to stop the countdown) to remember just what these weapons are and where he has seen them. Mirya is strongly suggested (and believed by fans) to have died in childbirth while giving birth to Maia. The behind the scenes reason for these deaths is highly suspected to be Harmony Gold's move to phase out usage of the Zentraedi and other recognizably Macross elements from Robotech canon due to licencing issues.
A big reason why Avengers Arena is so controversial is this happening to... pretty much everyone who dies. Juston, Mettle, and Red Raven all get killed after having barely any focus and are mainly used as plot devices. It also reeks of Deus Exit Machina; all of said characters are powerful enough that the only way the plot could function is to get them out of the way before they could get a chance to curb-stomp Arcade into dust.
After a prolonged absence, the cast of Supreme Power showed up in New Avengers just to be unceremoniously slaughtered by Namor and his new Cabal. To add insult to injury, the Cabal then blew up the Squadron's planet.
Block 109: Otto Skorzeny, who's something of a Memetic Badass of World War II, is unceremoniously killed by Slashed Throat after he boasts that he's the local SS commander to a member of the Teutonic Order.
Feydriva is rather suddenly killed off in the third album while the heroes visit a Vanishing Village.
Fratus Sinister looks like he's going to play a major part in the final battle between Wismerhill's and Haazheel's forces, but he's casually killed by Hellaynnea.
Dinocorps: Buzz was, at best, a Mauve Shirt with a few lines, but he was still a member of the eponymous crew. When he finally does something noteworthy, he's shot out the sky by Icks or Blix and seldom mentioned afterwards.
Despite being a main character in The Multiversity Guidebook #1, the only clue to the fate of Earth-42's Dick Grayson fate in The Multiversity #2 is during a brief montage, where it's shown that he was hanged by the Atomic Knights.
Cyclops got an infamous off-panel death, as shown in Death of X.