The Trickster was a minor-league crook from Central City whose criminal exploits were frequently opposed by the Flash. His main M.O. involved a variety of 'gag' weaponry, often based on classic comedic props.
The Trickster was perhaps not so much evil as he was deluded, apparently suffering from a psychiatric disorder that could ordinarily be treated with medication. When off his medication, James Jesse would revert to his 'villainous' persona and begin wearing his Trickster costume (evidently without being fully aware of the fact). The Flash actually enjoyed a fairly friendly relationship with Jesse, and was able to reason with him even in his delusional state.
When the Trickster hooked up with three of Flash's other rogues to enact vengeance upon the speedster, Flash was able to 'talk him down' and get vital information on the others' plans. Jesse even agreed to return to the hospital at Flash's urging, raising his drink in a toast to the Flash's 'victory'. Flash promised he'd come see him and play soft-tip darts.
Voice actor Mark Hamill previously portrayed the Trickster in two episodes of the 1990 live-action television series The Flash and later reprised the same role in the 2014 live-action television series The Flash, both set in the Arrowverse. The animated character design blends elements of Hamill's costume (mainly the multicolored hair; Trickster is blond in the comics) from that series with the character's classic comic-book design; the animated version's facial features even suggest those of Mark Hamill.