The Joker, immortal?
Taskmaster: Unthinkable gives a more in depth look at the villain Taskmaster than has previously been seen in comics. Taskmaster's usual role as the leader of a school for henchmen is abandoned as the villain struggles against waves of enemies, most of whom he trained, in an effort to prove his innocence.
Shazam Vol. 1 (The New 52) provides an origin story for both Shazam (a.k.a. Captain Marvel) and Black Adam.
"The Death of Iris Allen" story arc marks the beginning of the end for Barry Allen, The Flash.
The Flash Vol. 1 #324, The Flash is corrupted by Professor Zoom, fear, and love.
Batman Vol. 1 #251 "The Joker's Five Way Revenge" shows The Joker making good on a promise... a promise of murder.
Batman: Shadow of the Bat #38 provides an origin story for The Clown Prince of Crime.
While Batman: Shadow of the Bat #37 does not feature The Joker as a prominent character it is, almost entirely, about him. The inclusions of medical records and psychiatric files give a lot of insight into the mind of the Clown Prince of Crime and make this book a necessary read for Joker fans.
Thanos Rising issues #1-5 have been thoughtfully compiled into one graphic novel titled, simply, Thanos Rising. The collection is an enthralling origin story for the villain called Thanos- often referred to as "Thanos the Destroyer" or "The Mad Titan".