No, you don't need a key in the "hard version" to get in the "doggy-door".
Simon2: you had to get past the monster with a 1000 eyes and a 1000 ears. The eyes part was easy, you just had to cut the power. But to sneak past it was a bit harder. First you had to go to the role-playing nerds and transform one nerd into a puppy. Then you go to the monster and "wear puppy". The puppy will then transform into "puppy-slippers". Logical? No! Funny? yes!