Revenant is french for return as in the return of Willie Watt.
This is the second episode in a row that deals with people with mental powers, after "Mind Games".
Bruce makes references to immortals in the Batman: The Animated Series episode "Avatar", and witch boys and demons in The New Batman Adventures episode "The Demon Within", and would face (production-wise) zombies in Justice League.
Willie's vengeance on Nelson, his crush on Blade, and the accident he had with the GoLeM that he attributes his powers to follow the events of the episode "Golem".