The Prankster is Joker, essentially. More someone who plays cruel (homicidal) jokes on people than someone who likes to torment via impossible brain teasers (ah, Gryffindors...riddles are not quite their forte). Death Mask is Black Mask, but he stole the aspect of Joker that pairs him with an obsessive female sidekick with corresponding theme. Aaaaand, since you're familiar with the Batverse, you just may recognize who the villain of this particular tale is fashioned after. His origin story is being blatantly ripped-off. The fear element should be a giant hint. ;)
Funny you should mention Nightwing and Robin... We haven't seen Harry in this yet, have we? Mwahaha.
Glad you're liking it thus far. More action and adventure to come. Same Bat time, same Bat channel!