Big's cameos in Secret Rings can be quite amusing, but the real funnies come with the diary pages you get for triggering them. Among the things he did while in the story book include attempting to fish in a desert and somehow holding a conversation with a skeleton who (according to Big) was once a colorful fish that could sing. Maybe the heat had gotten to him?
King Solomon's appearance after Erazor Djinn dealt with him. He's a disembodied skull that can only hop around and talk to people.
King Solomon: I am the great and powerful King Solomon!
Sonic: (grinning) If you say so...
The ending, where Sonic wishes for Erazor to be permanently imprisoned in his own lamp (after wishing for Shahra to come back to life then restoring the Arabian Nights). Not only is seeing Erazor painfully humiliated and getting his comeuppance hilariously awesome, but the genie is reduced to pathetically begging Shahra, who he had previously murdered, to stop him, then asking her for a second chance. The way Sonic sighs and shakes his head sells it — a nonverbal: "Dude, she's not taking you back. It's OVER."
The Black Knight
The opening scene of Sonic and The Black Knight: Sonic gets warped into Camelot, holding a pair of chilidogs, which he makes a diving save to keep from falling. After eating one, he then demonstrates his speed by tossing the other one up in the air, routing all of the Mooks in sight, and then catching it.
Sonic's reaction at meeting the "Lady of the Lake" for the first time, here played by Amy. He's about to bolt until Caliburn stops him. Throughout the whole meeting, Sonic has an uneasy look on his face.
Sonic's reaction to saving the little girl's family, only for it to be the Lady of the Lake in disguise. And Caliburn thought saving innocent townspeople from a dragon was going to deter them.
After Sonic defeats and subsequently saves Sir Percival — Blaze the Cat — Caliburn tells them to save "the hugs and kisses for later". Instead of getting flustered (though Percival did blush), Sonic asks Caliburn if he's jealous, to which the sword splutters an unconvincing "of course not".
At one point during gameplay in Black Knight, you have to grind some railing over lava, prompting Caliburn to comment on how easy it'd be for them to fall in.
Sonic: I know, isn't it great!?
In retrospect, it's pretty funny seeing a hedgehog having an argument with a sword.
The look on Sonic's face when he's told he's the real King Arthur.
After the credits in Black Knight, Sonic is telling Amy about what happened. She doesn't buy it, and thinks he's just making up excuses for missing a date with her, and not only did she get Stood Up, she's also displeased.
On that note, this is the last we ever hear of Jason Griffith as Sonic considering the voice actors were replaced starting with the third Sonic Riders game. The fact that Jason's last words as Sonic are panicking and begging Amy to put down her hammer, especially compared to Ryan Drummond's last Sonic lines in Sonic Heroes, can make for some decent Black Comedy.
In the cutscene after you defeat King Arthur for the first time, Caliburn dubs Sonic 'Knave the Hedgehog' after Sonic tells him to stop calling him 'Knave.' Sonic's response? Calling Caliburn an oversized letter opener.
Before that in the same cutscene, Sonic and Caliburn start arguing. Then King Arthur insults Sonic by saying he isn't worth slaying. What makes this funny is that Caliburnagrees with King Arthur.
King Arthur: Ha! A fool of a knight. Not even worth slaying.