Perhaps it could be via a supermoon?

If you're planning on doing Sonic as the werehog TF~

Sonic finding a chili dog on a nearby table
Sonic's arm suddenly stretching to grab it, his arm getting furry as his gloves shred
And the rest is a normal TF into the werehog~

He'd most likely be shocked at first, but moreso annoyed by the end of the TF.

If you enjoy the idea, let me know through our DMs so we can talk about it more~

Oh, sorry, I forgot to mention that. The subject isn't gonna be Sonic.

Ah~ Any character in particular or are we leaving it vague?

Well, I was planning to ask for other people's OC to use it as a subject, a human subject.

First I would suggest someone bashing the sonic game that did it like “their ruined sonic” maybe after watching a video or playing a game the character look at him with the look of oh you think we’re hog are terrible I’ll show you”

Or maybe depend on his reaction can be annoyed because he a werehog or if he love the game or give it credit maybe the spirit of the game will turn him.

Or someone who drawn their own character turn themselves into a werehog or have someone else like who like to draw heard their complain about drawing werehog and decide that it time to do some editing by redrawing him as a werehog out of spite and his judgemental attitude

Two dark Gaia monsters are playing tug of war with a guy's arms when his arms start stretching out and he tfs. The dark energy the monsters expell starts changing the guy into Werehog and once fully tfed he throws the monsters away.

Something that might be cool, how about having his picture taken and he starts transforming from there. Something like from those Goosebumps stories involving camera and the picture showing something different and the subject in the picture changing into whats on that picture. It would make a cool call back to the animated short that debuted the Werehog.

Your human character can be shocked and confused at first and then starts to enjoy being becoming an all powerful muscular Werehog.

Easy: Have the guy to be TFed finding a pair of spiked cleats, trying them on, and then transforming from his feet upward into the Werehog. As the transformation goes, the subject goes from scared, to surprised, to amazed, to growling with delight as more of his body becomes covered with werehog fur.