But seriously, folks. If you're mentioning Mortal Kombat because of its notoriety for over-the-top blood-and-gore violence, Nintendo isn't going to do that with its brand.
EVER.

... Or, if you're referring to the "traditional fighting game" design with two characters beating each other up in a functionally empty 2D/3D arena until one fighter's HP hits zero, that openly contradicts what makes Smash Bros. Smash Bros.

Because it's not about the characters.

The key feature of Smash Bros. is that it's sort of a hybrid of a fighting game and 2D platformer. You always have to consider the terrain, even if the only mode you play is Final Destination No Items Fox Only For Glory. Your characters do not have fixed HP because HP doesn't determine the winner - what determines the winner is who is able to actually remain on the stage, or return to it after taking a hit. When you take a hit, you receive knockback / recoil from the hit, but the amount of recoil increases with each successive hit you take. This does mean that for every character there is a certain, unofficial threshold beyond which taking a (strong) attack will usually kill, but again, this depends on terrain. Did the recoil knock them in the proper direction for a KO, or are they able to make a comeback?

And again, it's not about the characters. Look at Brawlout or Rivals of Aether, two games that mimic the underlying Smash Bros. formula (i.e. damage percents and recoil) but with their own all-original casts.

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