If I was a kid and I got a Muppet game where I couldn't play as Kermit, I'd be pissed. That's the world that Muppet Monster Adventure forces on us, one where people know who Robin the Frog is. The good Muppets have been kidnapped by an evil monster, and it's up to Robin to rescue them, maybe? This is a bog standard licensed platformer, and it's not especially terrible as those go.