Here's a design doc that has some of them, at least. We had models and voices already set up for most of them: https://docs.google.com/document/d/1nptCYY5MiCcLD5i2eOZErvobD4an3MyczJiIkmWKeYI/edit?usp=sharing
Easy/Medium/Hard is in implementation time, not how they are to play against. The easy ones I could do one or two a day at least, and the Hard ones might take me a day or three (depending) for one of them.
Then it was a matter of designing rooms/chunks to really exploit all of the interesting mechanics here, and moving on from there.
The plan was never to have raptor upgrades or whatnot, but rather to really go for making the enemies interesting and puzzle-like. There are a lot of games where you don't get a whole lot of upgrades and nonetheless things stay very interesting. I would argue that the Mario games stay that way: sure they have upgrades, but for hardcore Mario players it actually is the level and enemy design that's most interesting, and playing permanently as small mario can be the most interesting and tense challenge.
That said, I was open to potentially doing some upgrades or whatnot if the game was attracting a lot of people who wanted it. It wouldn't have been hard to do, but it was just a bit counter to the pure "feel like an actual raptor" experience I was going for.