He is one of the Frontier Brains of the Battle Castle in the Sinnoh and Johto regions. Darach is the host and caretaker of the Battle Castle, managing CP awarded to or spent by Trainers under the orders of Lady Caitlin. As Caitlin's butler, not only does he manage the Battle Castle but he also battles for her in her place and acts as the Frontier Brain of the facility. Darach will challenge the player on their 21st consecutive battle and award a Silver Print if defeated. He will battle the player again if the player reaches the 49th battle, this time handing out the Gold Print if defeated.
Darach has these Pokémon when he is challenged for a print:
This section is incomplete. Please feel free to edit this section to add missing information and complete it. Reason: needs a list of the quotes determined by the amount of CP earned.
After winning a battle
"<player>, good show. A hard-fought win, yes? Lady Caitlin has instructed me to award you x CP."
"<player>, well done. A quite remarkable victory it was. Lady Caitlin has instructed me to award you x CP."
"<player>, bravo. A fantastic victory, to be sure. Lady Caitlin has instructed me to award you x CP."
After clearing seven consecutive battles
"Congratulations on clearing seven consecutive battles. For your valiant effort, <player>, please accept this BP. We'll return any items that we were holding for you."
"Welcome. I am Darach, as you know, and I am the Castle Valet. Lady Caitlin, my employer, is not one to accept defeat willingly. However, for a reason I'm not at liberty to disclose, she cannot battle. Consequently, I will do battle in her ladyship's place. ...Let me assure you that you won't be shortchanged by facing me. En garde!"
"My Pokémon could not be faulted in any way or form. My hat's off to you."
After being defeated
"<Player>, you are truly in possession of a superlative talent! I drew on every reserve of experience and etiquette handed down through our heritage of glorious servitude. But even then, I failed To fend off your inspired and inspiring challenge. I shall see to appeasing Lady Caitlin's displeasure at my loss. <Player>, please do return to our Battle Castle. We will be delighted and honored to have you back!"
"Your mastery of Pokémon is as breathtaking as ever. <Player>, you certainly are to be commended. ...However, if I may say so, I noticed something about the way you battle. After all, I have the opportunity to watch you closely firsthand. So, what is it that I noticed? As a Trainer myself, it is but proper etiquette to show you in a battle. Let us begin! En garde!"
"Your skills are superlative as ever! My admiration knows no bounds."
After being defeated
"I am humbled... What I'd perceived to be a weakness was only illusory... Or, perhaps you corrected it in the course of our battle. Regardless, your performance was stunning again. Though she cannot say it, Lady Caitlin appears quite taken by your style. For her sake at the very least, please do return to our Battle Castle!"
Darach appeared alongside Lady Caitlin in the Platinum chapter. Darach first appeared when Platinum started her challenge of the Battle Castle and was in charge of giving her Castle Points while Caitlin watched the battles. Once Platinum manages to win enough battles to face the Frontier Brain, Looker is shocked to find out that Darach is in fact, the Battle Castle Frontier Brain instead of Caitlin; Darach and Platinum then begin their battle.
In battle, Darach seems to have a different personality, this is shown when he drops his calm demeanor and starts laughing manically while confidently stating that he will win the battle. Despite the power his Pokémon possessed, Darach is eventually defeated once Platinum learns to manage money properly to find out his weaknesses.
Gallade first appeared outside of the Battle Castle, acting like Caitlin's bodyguard. During Platinum's battle with Darach, he was the first Pokémon used in their battle. He managed to defeat Platinum's Rapidash and Lopunny, but was defeated when Lopunny's Cute Charm prevented him from dodging a Dizzy Punch, allowing Empoleon to take advantage of his confused status and defeat him.
Staraptor was the third Pokémon that Darach used in his battle against Platinum. It used confusing moves and kept healing itself in its battle against Platinum's Empoleon, but was defeated when she froze it with Blizzard.
Darach's Pokémon Cards listed with a blue background are only legal to use in the current Expanded format. Cards listed with a silver background are legal to use in both the current Standard and Expanded formats.
However, Double Battles had not yet been introduced in those games at the time.
Darach's in-battle sprite has the most frames of any animated sprite in Generation IV, with five as opposed to the usual three.
Darach is the only Generation IV Frontier Brain with a signature Pokémon: his Empoleon.
An NPC in the Battle Castle says, "Mr. Darach... His feelings for Lady Caitlin are all bottled up... Oh, how I pine for him..." which implies that Darach has feelings for Caitlin, but refuses to show these emotions to her.