It'd be hard to draw a line there. You'd have to determine what part of the IP you are referring to. That's why I was saying sequels and spin-offs would have to wait until the franchise copyright expires, rather than the individual work expires.
This is where it starts to get really complicated.
The safest answer would be that you need to wait until both the copyright has expired AND the trademarks on all the characters, logos, and other distinctive elements have become dead and ceased use in commerce.
It is not enough for the trademarks to die due to lack of use, since copyright will persist until you are dead. Even if your descendants want to use the material after copyright expires, trademark protections exist as long as it remains used in commerce.
Let's do a little thought experiment with that.
There are a few people who argue that the original Steamboat Willie, Plane Crazy, and Gallopin Gaucho cartoons expired because of their first screen audience release dates and published copyright information. Let's use that rather than Super Mario Bros for the first part of this thought experiment.
If these were in public domain today, you could make copies of the original works. The first step would be to track down one of the 1928 films. You couldn't use any of the many re-releases because they touched them up, cleaned the audio, repainted some bad frames, and those later re-releases are not public domain.
Next, you would only be allowed to use the 1928 version of mickey mouse. He looked very much like a mouse, radically different from today's mickey mouse. You could derive from the black and white Mickey rodent wearing overalls, the Minnie rodent wearing a skirt, Pete the cat, and Oswald the rabbit. All of them would be the 1928 versions, not the 2015 versions.
You could not use any of the trademarked terms or trademarked logos since trademarks persist as long as the thing is used in commerce. Even though the 1928 film would be useable as a copy, you could not create your own Mickey Mouse line of products due to trademark rules. Similarly Minnie and Pete are both names covered by trademark.
So now bringing it back to Mario.
Wikipedia tells me Mario first appeared in 1981 in Donkey Kong (then called "Jumpman"), Luigi in 1983 in Mario Bros. Assuming no other changes, that version of Donkey Kong will enter public domain in 2077, and that version of Mario Bros will enter public domain in 2079.
So fast forwarding to 2079...
For convenience, assume all the characters in the franchise are still in active use, trademarked, and no other changes to law have happened.
You could make and distribute copies of the original Donkey Kong published in 1981, and the original Mario Bros published in 1983. It was made for arcade machines, and by 1983 had been ported to a few systems.
You could make derivative works using those characters and those old stories, but not making use of whatever advancements have happened between 1984-2079, those are still protected.
You get the original blue/red/orange Jumpman/Mario, the white faced (remember Japanese beauty) red-head pink dress "the Lady" (later named Pauline), the two-tone blocky Donkey Kong, and the blue/orange/green Luigi, as they appeared in 1981 and 1983, not as they would be depicted in 2079.
You don't get any story developed between 1984-2079. They were brothers as established in 1983, but any story revelations or changes made after 1983 would be off limits until they enter public domain.
You could not use Princess Peach or Daisy or any other modern characters, because they had not been introduced before the 1983 cutoff date you have in 2079.
Assuming the names are trademarked and used in commerce in 2079, you could use the names in a direct clone because that is from copyright, but could not make your own product with the same names or iconography covered by trademark in 2079.
So if you're alive in 2079, and you still have some really old arcade boxes or Atari 2600s or whatever else they were ported to, or someone manufactures those devices in 2079, then you can make all the copies you want since copyright will have expired. Your rights to make clones and similar products may be somewhat by trademark and other IP laws, but direct copies could be enjoyed by anybody.