A host of weird, undercooked ideas in DKC3.
Kiddy can smash through cracked floors if thrown upward. This is used maybe twice.
Kiddy can bounce on the surface of water like skimming a rock. This is used maybe twice.
Ellie is scared of rats and panics in the opposite direction when she sees them. This is used maybe twice.
Hero Coins are now carried by an enemy named Koin and used as a shield, requiring them to be hit from behind with a barrel in order to get their coin. Clever idea. But mostly, they're just stood in front of a wall, so you throw the (often infinitely respawning) nearby keg at said wall, getting it effortlessly. It's actually rare that there's any strategy required besides this.
Long, banal games of Simon hidden in invisible caves on the world map. Crackers.
Dull as ditchwater fetch quest with the Bear brothers all over the map.
Just generally gimmicky as all get out, with tons of bizarre stuff like the level with the fish you have to feed, the level where you move in super slow motion and jump high, the level where your controls are reversed, etc etc. Worth playing once, though.