When Dr. Eggman had visited the cafeteria where Dave worked, Dave put an expression on the doctor, who then stated him as a helper and led to his base. Dave wanted to become an evil genius, praising Dr. Eggman for his achivements and status, but the latest forced him to do such primitive things as cleaning the base. On his duty, he heard chat of envying Orbot and Cubot and then dissassembled Cubot, leading to Orbot to use help of Sonic the Hedgehog.
As Dave tired of his work and asked Dr. Eggman for higher job title, the latest asked him to wait several weeks for it. Dave became enfuriated by it and then locked himself up in the workshop to do a Doomsday Device equal to the one which was created by Eggman himself. As Sonic and Tails made both geniuses to overpower their machines, the energy from them created a black hole which was erased by Sonic.
As for Dave, due to his actions, Dr. Eggman fired him from the post of his intern, leading to Dave's returning to the cafeteria, swearing for revenge to both Eggman and Sonic.
Dave appears as a cameo, still working in cafeteria as Eggman stole a sandwich he ordered to not pay for it, while being depressed. Dave is shown to take Eggman neutrally, but they are not full-fledged enemies, the same as with Sonic.
How to succeed in evil without really trying
Dave appears to be one of the leaders and the main mechanic of evil organization "Lightningbolt Society" who invites Tails to join him, as he saw his invention to cause random and pointless destruction they admired. Dave plants evil seeds in place of Sticks's destroyed garden and later they were attacked and destroyed by the heroes. In the end of episode, he is taking a sandwich with his own seeds, which could lead him to a sad fate, as they grow into giant monsters.
Dr. Eggman's Tomato Sauce
Dave still works in cafeteria and was one of people to try and buy Dr. Eggman's Tomato Sauce. He also threw several jokes when Sonic visited the cafeteria. After Eggman used the cans of the sauce to reprogram all mechanic to attack people, Dave was attacked by his cashbox only to be saved by Sticks.
Dave made several cameos during the show before his another big-time villain role in "Eggman Unplugged", once again, him to be a member of evil Lightningbolt Society. He, the supreme of the society and two other members take over Dr. Eggman's Lair once he decided to unpluge all his mechanisms (excluding Orbot and Cubot). As the members of Society didn't know how his system worked, they created mass mischief, firing Octobot, Bee-bots, Cowbot, Eggman's Rocket and Lair's defense too random, complicated and intense for heroes to beat it.
Accidentaly, Dave deactivated Orbot and Cubot, leading Eggman to join the heroes and give the Society the misinformation, that heroes are going to enter the secret backdoor, while they entered the lair through unprotected front door. As the members of Lightningbolt Society tried to use the guns they found, Dr. Eggman deactivated them using his portative device and Society left the Lair.
Next Top Villain
Dave returns as the main antagonist of 37 episode "Next Top Villain", dreaming of his evil unlimited powers, challenge Team Sonic and winning by freezing Amy and Tails, having bears to follow Knuckles and Sticks and kill Sonic himself by laser fire. He is then interrupted by his mother-villain, who states that he is not evil enough and Lightningbolt Society are having not evil influence enough on him, forcing Dave to go and prove his villain stat. He tries to freeze, dry and having cute animals attacking Team Sonic, all backfiring at him. He was then mocked by Eggman, who showed him his new electromagnetic cage. Accidentaly, enraged by joke, Dave activates lasers of Egg Mobile which crush the palm which falls on Eggman.
Dave from now takes the role of villain and states it through TV-message, having Eggman defeated in his cage, but he was mocked by Sonic on TV. During chating with Eggman, Dave decides to revenge using Eggman's Octopus-Bot, dreaming of fighting Sonic and him begging for mercy, only to find out he doesn't know how to control it, being mocked even more. By the time Sonic frees Eggman (as the sneak past Dave's Mom) Dave starts to learn the control, but he made selfie with a flash, shocking himself and trembling Octopus-Bot when Sonic tried to attack the weak-spot. This led Bot to crush Dave's house with his mom in it. As Octopus-Bot was deactivated, Dave went to check his mom calling, only for her being proud for him wrecking chaos and even destroying the house, calling him worth of "villain" title, much to Dave's enjoy.