It is unknown when, where or how, Tobias managed to capture Darkrai but it has been implied that he has owned it for some time. According to rumour, Tobias had defeated all of Sinnoh's Gym Leaders using only Darkrai. The Legendary Pokémon defeated almost every opponent it faced in the Lily of the Valley Conference and was considered to be virtually unbeatable. Ash Ketchum is the only known trainer in the entire Sinnoh Region that has managed to defeat Darkrai.
During their battle, Darkrai faced off against Heracross first, who was able to turn Dark Void to its advantage by using Sleep Talk to use a super effective Megahorn. Darkrai managed to endure the blow and knocked out the still sleeping Heracross with a single Dream Eater. It then used its superior Special Attack power to overwhelm Torkoal'sFlamethrower, and Torkoal itself, with a single Dark Pulse. Gible managed to land a Rock Smash and avoid Ice Beam before firing a Draco Meteor but with an impressive display of Speed, Darkrai avoided every single meteor and defeated Gible with Dark Pulse. Having lost three of his Pokemon, Ash used his extremely powerful Sceptile, who endured Darkrai's Ice Beam and woke up remarkably quickly after being hit by Darkrai's Dark Void although it had to endure a Dream Eater in the process. Sceptile was notable for being the only one of Ash's Pokemon that endured two of Darkrai's attacks despite one of those attacks being super effective against him. Sceptile finally managed to defeat Darkrai with a devastating Leaf Blade. Despite this loss, Tobias' next opponent was no match for Darkrai, who defeated all six of his Pokémon single-handededly.