I was not prepared for this to be dropped right now, and would have preferred this been done later, but here we go I guess.
As far as low ends go Mario has been KO'd by feats ranging from 9-B to 8-C, I don't think it's fair to go with the low ends, so I'd rather not go with that. However, the anti-feats for a cosmic level Mario are so staggeringly high I think it's absurd to place him there, not only that but placing him above Tier 6 would result in Mario and Bowser having to scale ABOVE amped Bowser which I find ridiculous, so unless it's decided to drop scaling from the series entirely which I doubt will happen, Tier 6+ Mario should happen. DKs Moon feat shouldn't scale to the Mario cast and DKC should be given a separate key, plus its ludicrously stronger than
the most powerful punch Bowser ever did (Which he did when heavily amped amped to the point where he was stronger than a character who could one-shot him in base)
For Tier 7 we have the bye bye canon feat,
which was calc'd at 294 kilos (The force of which is taken casually), the moon cannon feat,
calc'd at at 2.93 megatons, and if you want to accept the old Castle Punt calc, that's also in the megaton range, as is the Stadium Explosion feat calc'd by Death Battle to further back up Low 7-C to low 6-C ratings (Low 6-C being supported by Dark Bowsers storm, which Bowser is forced to struggle against, while most of the Tier 7 feats are casual). This rating is probably the most solid in my view, as it avoids the redundancy of characters scaling to their own amped forms, while not having them at 9-B getting knocked out by falls something that is very common in the series.