Viability - doing well so far! One major thing I noticed is that once the game starts over it doesn't reset the affection variable, so you are automatically best friends with the griffin as soon as you start to interact with it.
Presentation: I would recommend proofreading for spelling/grammatical errors, but other than that things are solid! I also think you should potentially change the color of links that have already been visited.
Theme - I like the colors, feels like the sky, which fits well. Styling the affection variable somehow would look really nice.
Engagement - I was engaged! Could easily be longer/have more to do; maybe different levels of friendship with the griffin as affection goes up before best friend?