Zoom killing Barry's wife.
Hal Jordan going crazy and killing the corps, then using his Zero Hour powers to retcon some bullshit bug explanation.
Clone saga. Like it or not, it was a damn big plan that fucked up Peter Parker's life for a year.
Lucifer's destruction of the Mansions of Silence has been mentioned.
Whoever the fuck hired Puck and Loki to kidnap Daniel, which ended up causing Morpheus' death.
