Driven to Madness / Go Mad from the Revelation: Something like it. Though others have a limited ability to do it, he has the most ability to give enemies insanity, a sort of nonstandard status effect. Insane enemies behave differently (usually becoming less tactical but more damaging), and Cthulhu and some other party members can draw strength from their insanity.
Face-Heel Turn: In the fake-out ending, when his curse is broken, he unleashes his foretold terror upon the world. Subverted when the narrator reluctantly rewrites the ending, and Cthulhu embraces his heroism.
Fourth Wall Observer: He chats/argues with the narrator every now and then. For example, he would have never learned how to break his curse unless the narrator blabbed about it.
Magic Knight: The degrees of "magic" and "knight" he attains depend on how you handle his branching level-ups. Generally speaking, he's got higher Magic, Will, and MP than Sharpe, but lower Strength, Vitality, Agility, and HP.
Pragmatic Villainy: He intends to become a hero only because he wants to gain his power back.
"You're a dark fiend? You should have told me! That's so sexy!"
Personality Blood Types: Parodied. She explains herself as blood type B and explain what that means for her personality, then asks the others what their blood types are. Given what theotherpartymembers are, she is...unsatisfied with the reception. Even the other twohumans in the party don't give expected answers.
Dropped a Bridge on Him: Paw's brief appearance in Cthulhu's Angels consists of him being vaporized by a death ray after the first line of his introduction. It seems the U-Bovinator is a bit more Dangerously Genre Savvy than Pawz.
Screw This, I'm Outta Here!: In Chulhu's Angels, he appears to reprise his role from the original campaign as a boss, but bails when the Dark Dragon shows up.
Unskilled, but Strong: He has monstrously high stats, but a low amount of special abilities and no way besides a Union to do multiple hits, so he's rather less useful than other party members. However, his Volcanic Aura still synergizes nicely with October's fire spells.