In the instruction booklet for Super Mario Bros./Duck Hunt, it does in fact explicitly state that the Koopa (plural) invaded the "peaceful" mushroom kingdom and turned the Mushroom People into stones, bricks, and field horse hair plants. This would of course be illegal in nearly all jurisdictions in real life if such practices were physically possible. So one cannot argue that this fact alone makes the Koopa appear to be the aggressors in this narrative.

I know what you're thinking; "But King Koopa kidnapped Princess Toadstool so doesnt that make him the bad guy by default?" Well no one can argue that she was clearly being held against her will. It is clear that King Koopa knew what he was doing and it is clear through the dialogue in the game that she wanted to be rescued.

However... we don't know the full story about who among the Koopa were transforming the "peaceful" mushroom people. The booklet mentions the use of black magic however it is not clear whether King Koopa used the black magic himself or ordered one of his underlings to do it (just as evil) OR there was a rogue actor in his party who was doing the transforming and King Koopa didn't necessarily like what said actor was doing.

But if we simply go off what transpires in the game rather than speculate on what happened off screen or prior to the game starting, Mario himself was not acting with the best intentions. For starters, the game requires you to kill (yes *kill*, the booklet definitively states that these defenseless Little Goombas and Koopa Troopas are DYING a horrible death as Mario curb stomps these creatures into nothingness. Are we assuming the role of a fearless plumber or Derek Vineyard from American History X?) and you are not killing just one of these creatures but dozens, potentially hundreds if you play through all 32 levels. Do these fragile lives not matter? Do they not suffer and feel pain the way that we do? What was that first Goomba doing before Mario and Luigi showed up? Probably just walking to some dark area to relax and maybe grow on something decaying (I dont know, how do Goombas eat food anyways??)

In a legal sense, the killing of the first Goomba was completely unjustifiable. Sure if Mario doesn't move, the Goomba will kill him, but is it not possible for Mario to jump over him and avoid him entirely? The closest scenario I can think of in real life would be if someone was walking toward me with a knife in hand. I can choose to pull out a gun and kill him after believing him to be a threat, step off to the side, or run away. We don't know if the Goomba had any sense of what he was doing. Clearly from the other Goombas, they dont seem to have any purpose at all because if left alone, they walk off a ledge into their deaths. Hardly seems like they are on a mission. I'm just saying that it's easy to side with the guy rescuing the Princess until we consider that many of the creatures here could simply be in the wrong place at the wrong time.

Mario at best is a vigilante, taking out everything in his path, collateral damage be damned. Those Spiny's that Lakitu throws out are simply Lakitu's pets. If a serial killer throws his dog out the window to try and stop you, is it okay to kill the dog?

The tricky part of all this is the simple fact that merely touching any of Mario's enemies in this game is instant death. But does Mario know that going into this adventure? I would think it reasonable to shoot someone in real life if he was rushing toward me and I knew that if he even grazed me, I'd die instantly. But for Mario, there's no way he could've known that if he never encountered these Goombas before. He just figured it was better to shoot first, ask questions later.

Another element we don't hear about is the fact that if the Koopa transformed the Mushroom People into bricks, doesn't that make Mario a mass murderer?

Now don't get me wrong, maybe there are no police or military in the Mushroom Kingdom. maybe Mario IS the police. but just like in real life, proper escalation of force is standard protocol. Does killing 100 Goombas justify the saving of 1 Princess Toadstool?

Also, did King Koopa have some sort of beef with the Mario Bros. before the game started? The booklet says the Mushroom Kingdom was peaceful, but that is a pretty subjective term. Peaceful because their ancestors killed everyone they needed to and now the descendants no longer have to kill their enemies? What does peaceful mean these days? Maybe they were peaceful for a while but they initially were the ones who raped and pillaged the Koopa Kingdom?

Just lots of questions unanswered here and I find the idea of "an eye for an eye" in Mario's savage quest of revenge to be quite disturbing