Warning: contains spoilers for The Flash #776!
While the most famous fourth wall-breaker in comics is undoubtedly Marvel's Deadpool, DC's Flash is about to give the Merc with a Mouth a run for his money. One of the very few characters with the unique power of "comics awareness", Deadpool is acutely aware that he's a fictional character in a comic book, completely at the mercy of his writers. But in The Flash #776, the same power is granted to Wally West, via DC's equivalent of Doctor Strange: Doctor Fate.
Deadpool initially didn't break the fourth wall at all; he was created by legendary writer/artist Rob Liefeld in 1991 as a simple mercenary with twin katanas and a striking red-and-black costume design. It wasn't until the mid-2000s that other writers gave him his irreverent style of humor along with his signature ability to point out flaws and idiosyncrasies in his own writing. He would even acknowledge the reader from time to time - but Doctor Fate goes one step farther, and actively calls on the reader for help.
The Flash is dragged into a cave by Doctor Fate, who informs Wally that the two are trapped in a two-dimensional causeway and "...it's going to be up to you to guide us. To help us through." When Flash doesn't understand how he can help, Doctor Fate corrects him, pointing to the reader and shouting "YOU! The reader of this book! Our fate lies in your hands." At various points in the story, Doctor Fate insists that the reader turn the book clockwise, counterclockwise, and eventually upside-down, shifting gravity within the world of the comic. Doctor Fate and the Flash even climb from panel to panel, evading monsters on every page.
As an outside observer, the reader of comics is seldom taking action within the book. From a Doylist perspective, of course, the reader is not; the pages have been printed long before the reader ever bought a copy. Nor does the book account for a digital copy of the issue (Doctor Fate doesn't tell the reader to turn a phone, tablet or laptop, for example). Nevertheless, this is potentially one of the strongest powers in comics lore, showing that while Deadpool is content to make jokes about the meta-nature of his existence, Doctor Fate and the Flash actively use the reader to accomplish their goals.
With Doctor Fate having opened the Flash's eyes toward the fourth wall, Wally West is now aware of the world beyond the confines of his universe. The episodic nature of the current Flash run does not necessarily mean Wally will remember this encounter, however. Nevertheless, Deadpool no longer has a monopoly on breaking the fourth wall...for that honor now belongs to the Flash.