Celtic Guardian is one of the most commonly used monsters of Yami Yugi's Deck. A running gag that happens throughout the series is when Yugi Summons him, he replaces the adjective "Obnoxious" with a different one. Another ongoing joke has the Guardian reference the adjective in some way upon being Summoned or prior to being destroyed. (e.g. "I'm so bamboozled.") He apparently has a grudge against the Blue-Eyes White Dragon for spreading to others that he is a "weak monster", and has developed a complex as a result of that. In a rap battle between Yugi and Jaden Yuki, it is revealed that his name is allegedly Dave, and that he had difficulty stringing together coherent rhymes.

Episode Adjective Quote
"The Rebexorcist" Disgruntled
"Yami of Darkness" Frustrated "I am so frustrated."
"Dirty Dueling" Bamboozled "I'm so bamboozled."
"Penguin Ex Machina" Agnostic "I'm not sure what I believe in."
Cr@psule Monsters 3 Passive-Aggressive "God, I wish some people would stop posting on Facebook about cats all the time."
"Wait, what? Who's doing that?" (Yami)
"Oh, you know. Lots of people."
Throw Haga From The Train Sexually Frustrated "I'm so sexually--oh f*ck, I'm on a train!"
Right In The Feels Brainwashed "I'm so whatever he just said!"
Valley of the Duels Obnoxious Celtic Punching Bag "I'm so..." (cutoff)
YGO Kiwami Obnoxious Kill-Stealing "That's a nice kill you've got there. It'd be a shame if someone stole it."