"Destroy" vs. "Reduce to 0 or fewer HP"

When a card is destroyed by a destruction effect, it will be put into the trash (unless told otherwise, such as No Executions), without effecting its hit points in the slightest.

Yes, insta-kill effects (such as Sucker Punch or Sarabande of Destruction) will put the targetted card straight into the trash (unless otherwise stated). You can get around Apostate's flip mechanic this way if you use an insta-kill effect on him, since he flips if he has relics out and is "reduced to 0hp or fewer". If you're insta-killing him, you're not reducing his hp - you're ignoring them entirely.

Also matters for the Propulsion Systems in the MDP environment, which have (I think) 10hp and cause an instant game over if they are reduced to 0hp or fewer. If they get insta-killed, this doesn't happen - it's only if you deal damage to reduce the hp to zero (or fewer). Otherwise, villains like Spite would be impossible to fight in that environment.

If something is indestructible and its hp are reduced to zero or fewer, it will not die until its indestructibility is removed - this is most likely to occur in the Time Cataclysm when Fixed Point comes out. Anything which has zero or fewer hp when the card goes away will basically go "Oh, I'm supposed to be dead!" and will be destroyed at that point. If you go to zero or below while Fixed Point is out, but then heal back up into positive figures again by the time it goes away, you are fine :). Note that insta-kill effects will do nothing to an indestructible target. Also, characters like Mr Fixer, Omni-10, and the Naturalist can have great fun with Fixed Point, since "indestructible" means "cannot be removed from play by any means", so yay for multiple tools/styles/platings/forms :D. Note that if you take advantage of a Fixed Point to put out more stuff than you'd normally be allowed, its normal rules will kick in if you try to play another card of that type after Fixed Point goes away (meaning the cards you had in play will have to be removed as normal, no matter how many you had out).

You can totally destroy Character Cards.

There aren't too many cards that can destroy a Character Card, as most destructions excludes them (note End of Days and Cedistic Dissonant). Sucker Punch, Wrathful Gaze, Tire Iron, Fling into Darkness, and Cornered Beast can destroy Character Cards, but note that they are all cards that rely on the target to be below a certain HP value.

Viktor is the new greatest threat. Cause he destroys hero targets with 2hp or less. No THAC0, no Death Save, just go straight to dead ;)

Death's Grasp (in the Ennead deck) is similar, as that destroys any hero target with three or fewer hp if I remember rightly. Poor Mr Chomps :(.

Some villains can stop themselves being destroyed, however, such as Baron Blade, who flips when he "would be destroyed". I'm not sure whether this allows him to get around an Unforgiving Wasteland since that also overrides any "when this target would be destroyed" things by removing them from the game instead (which is absolutely epic against the Matriarch, especially if there is a Horrid Skunk Ape out - bye bye All of the Birdies in one go, and with no retaliation damage from Lilian as they are not being destroyed so she can't trigger off their removal). Maybe the "heroes choose the order of things" rule comes into play and you can actually have an unflipped Baron Blade get eaten by a Yeti or whatever :D.

Fright Train has one that destroys a hero target with 2 or fewer Hp too. Um. the throw one.

And I believe an incapped Osiris has similar.

Fortunately Osiris won't kill character cards.  He'll kill decoys and bots though.  With all the aoe damage and hits-the-lowest, Unity can have a pretty rough time.

Yeah, that's it, I remember now - he does only affect non-character cards (though there are plenty of insta-kill effects which don't). Which meant fighting the Ennead in the Block last weekend went pretty well, because the buffed-by-Rogues-and-many-cards-in-the-trash-from-several-Prison-Riots Time-Crazed Prisoners never lived long enough to do anything :D.

Unity can have a rough time against the Ennead, but she can also slaughter them. Most Ennead damage is 1 HP packets dealt to everyone, so Stealth Bot sucks all that up, saving everyone. An early Stealth Bot followed by a mix of other bots and a Fueled Shockwave can do 10+ damage to every member of the Ennead, with any platform bots or Mr. Chomps in play finishing off the survivors.

I'd say that Unity has a much better time against the Ennead than she does against Iron Legacy, who just destroys all her bots, full stop.

After reading the fairly large forum topic related to destroying Character Cards, I think a summary of the conclusion is that Character Cards are immune to any generic destroy effect.  By generic, I mean anything which states "destroy a card" or "destroy all cards."  Specific destroy effects would include "destroy a target" (a target is a specific type of card), "destroy an ongoing" (ongoing is a keyword for a card), etc.