Donkey Kong Country 3 was one of the last games to be released on the SNES. In fact, it's release coincided with the release of Super Mario 64 (1996) on the Nintendo 64. Occasionally when you go into Wrinkly's Save Cave you can hear a variation of the castle music from Super Mario 64.
In the Game Boy Advance version, there is a second lost world to the far left of the continental map. This second lost world is not in the SNES version.
This Super Nintendo game depicts a character named Barnacle Bear smoking a tobacco pipe in his cabin. It's unknown how it got past the Nintendo Censorship.
The Lost World name 'Krematoa' is a parody of the the volcano Krakatoa, which erupted in 1883. Coincidentally, when you achieve all the cogs and place them in the machine in Boomers Bomb Shelter, the colors inside of Krematoa (as well as every level inside) change to more orange and yellow colors. Meaning it could be on the verge of erupting. When you eventually return to Boomers Bomb Shelter, Boomer even makes a comment about how hot it is in there as well.
Kracka, the red version of Knocka in a TNT barrel exclusive to the GBA version of Doniey Kong Country 3, was actually created for the original SNES game. All of his sprites are present, along with an alternate red palette for the normal TNT barrel sprites which would have been used if he was picked up and thrown.