he is adopted by Bruce Wayne, who assists Grayson in bringing down the mafia boss responsible for his parents' deaths. The second episode in the season leads to Batgirl officially becoming part of the team, with each member divulging his or her secret identity to the others. This reveal eventually leads to Batgirl and Robin forming a sibling-like rivalry. One of the highlights of season 4 is the episode "Artifacts", which described a possible future in the year 3027. Featuring flashback scenes to 2027, the audience gets a glimpse of an older Batman, Dick Grayson operating as Nightwing (voiced by Jerry O'Connell), and Barbara Gordon, now reliant on a wheelchair and having become the Oracle (voiced by Kellie Martin). The episode also features elements from Frank Miller's The Dark Knight Returns, including the designs of both the Batman costume and the Batmobile. In the season finale, an alien invasion by entities called "The Joining" causes Batman to work alongside another superhero from the DC Universe and an original member of the Justice League, Martian Manhunter (voiced by Dorian Harewood), to thwart the aliens' plans. This is when Batman becomes part of the Justice League of America. More villains with new interpretations are once again introduced, including Tony Zucco (voiced by Mark Hamill, who voiced the Joker in the DC animated universe), Killer Moth (voiced by Jeff Bennett), Black Mask (voiced by James Remar), Rumor (voiced by Ron Perlman), the Everywhere Man (voiced by Brandon Routh), Harley Quinn (voiced by Hynden Walch), and Francis Grey (voiced by Dave Foley). The season also brought an end to Ethan Bennett's version of Clayface, including a storyline that redeemed Bennett by curing him of his condition. This gave writers the opportunity to introduce Basil Karlo's version of the villain (voiced by Wallace Langham in the first appearance, and Lex Lang in the second appearance). Season 4 also featured a redesign of Bruce Wayne, with a more square facial and chin structure, making him reminiscent of the DC animated universe Batman design. This was the final season worked on by Jeff Matsuda and Michael Jelenic, both of whom departed from the show after the season finale. Season 5 The final season on The Batman, season 5, focused primarily on Batman and Robin, with the pair teaming up with some of the DC Universe's characters to battle different villains. These team-ups included Superman (voiced by George