He is a character of the day who appeared in Round One - Begin!. Mandi was confident that Ash was going to be an easy opponent for the first round; however, due to his enormously over-inflated ego, he underestimated his opponent and had all three of his Pokémon taken out by Krabby, who evolved into Kingler during the battle.
He is a very popular Trainer who has many fans. One reason for his popularity is probably that he can perform magic tricks—for example, he made a group of Pidgey appear from nowhere.
His design basis is in the Juggler Trainer class, though his hairstyle is considerably different from them.
Mandi used his Exeggutor as his first Pokémon during his battle against Ash, while Ash chose to use his Krabby. Exeggutor first attacked with Psywave, forcing Krabby into the water. Exeggutor then used its Psychic attack to turn the watery arena into a giant whirlpool, trapping Krabby in the vortex. Exeggutor then launched a barrage of Egg Bombs to the vortex, producing a Wall of Water to keep Ash from recalling it. However, Krabby eventually managed to get out of the vortex and grabbed Exeggutor's leaves with Vice Grip, causing it so much pain that it became unable to attack and commence Mandi's order for using Hypnosis. Krabby then used Leer at Exeggutor and finished it off with Stomp.
Mandi chose to send out his Seadra as his second Pokémon in his battle against Ash. Ash's Krabby had just evolved into Kingler, but Mandi stood calm and told his Dragon Pokémon to use Agility. With its Agility, Seadra was easily able to dodge all of Kingler's Water Guns and some of its Bubbles, but it eventually got hit by a wide-spreading Bubble foam. The hit caused Seadra to fly into the air, and Kingler finished it off with Crabhammer.
Mandi send out his Golbat as his final Pokémon against Ash's Kingler. Ash told Kingler to dive underwater while Mandi commanded his Bat Pokémon to use Take Down. Kingler attempted to grab Golbat with Vice Grip, but Golbat evaded the attack by using Double Team. Golbat then launched a Razor Wind attack, hurting Kingler badly. Mandi was about to finish Kingler with Mega Drain, but Kingler launched a strong Hyper Beam at Golbat, knocking it out.