Okay, so I just had this awesome idea, what if Tower of Smash had different bosses depending on difficulty? (if Tower of Smash is real of course.) Here's some boss ideas I had, although I'm not super familiar with some of these franchises, so pardon me please. Alright, here we go! The Very Easy to Normal difficulty boss is on the left, and the Hard to Very Hard one is on the right.
10. Dino Pirhana/ King Boo
20. Yveltal/Giratina Origin Forme (I know he's already in a Pokeball, but I feel Nintendo wasted an opportunity to give one of the most intimidating Pokémon his coolest form.)
30. Tiki Final Boss thing from DKCR?/King K. Rool
40. Dr. Eggman/Perfect Chaos
50. Fire Emblem bosses! I have no idea....
60. Kraid/Mother Brain (Final form from Super Metroid.)
70. Starman/Porky (Would love to have used Gigyas, but it would have increased the age rating.)
80. Medusa/Hades
90. Marx/02
100. Master Core/New Tabuu form
Honorable Mentions: Water Wraith (Pikmin), That creepy *** clown final boss from Wario Land 3, Wham Bam Rock (Kirby) Rayquaza (Pokémon), Metal Overlord (Sonic Heroes), Dr. Wiley mech thing (Not super familiar with Megaman.), Black Shadow (F-Zero).
I think that having this kind of setup would add even more replayability if this mode was real.