10 Times Marvel And DC Secretly Crossed Over
2. Deathstroke Met Deadpool
Deadpool's creator Rob Liefeld has been happy to admit that the Merc with a Mouth owes a lot of his creation to DC's Deathstroke. It's a connection that fellow writer Joe Kelly was happy to parody.
Kelly also had a long stint writing Deadpool and decided to find a way to work him into the 2006 Superman/Batman annual.
In the annual, Superman and Batman wind up on a cruise together (the story is a reinterpretation of a SIlver Age story where they discovered each others' identity). The ship is then attacked by the Crime Syndicate of America, a team of supervillains from an alternate reality where the roles of heroes and villains are switched.
This time though, joining the evil versions of Superman, Batman and Wonder Woman is an alternate version of Deathstroke. This version is equally as proficient with a sword as his Earth-1 counterpart, but his personality is the complete opposite. Since Deathstroke is a calm and stoic professional, that means his doppelganger just so happens to be exactly like Deadpool.
The Earth-3 Deathstroke goes unnamed, but a running joke in the issue is that he keeps trying to say his name, only to get cut off after saying D-E-A.