SpawnShadow posted...
It helped that the original comic book of
Invincible
is completely owned by Skybound Entertainment, which series co-creator Robert Kirkman (probably best known these days for creating the also-Skybound-owned
The Walking Dead
) founded, with Kirkman and Skybound publishing the comic via Image while retaining the IP themselves. For a while in the '00s, Kirkman was
also
writing
Marvel Team-Up
over at Marvel. So, because he could personally authorize the use of his own character (or if not that directly, then easily convince the rest of Skybound to let Marvel briefly use the IP), and the issue would be published by Marvel, they gave him the go-ahead to write the crossover issue, which basically expanded on that lawyer-friendly cameo from
Invincible
's own book.
Unfortunately, the stars just didn't align in the same way for DC.
Based on how it was done doesn't seem they had permission to use batman either. Never fully shows batman and invincible never outright says batman.
DC did a similar thing with Deadpool. Brought in a deathstroke from a alt universe who was clearly crazy but anytime he tried to introduce himself he'd get out "dead" and promptly get interrupted by like being punched or something.