According to The Playlist, Wernick told the audience how, in order to use their version of Negasonic Teenage Warhead, Fox offered Marvel the chance to use Ego the Living Planet, who will appear in Guardians of the Galaxy Vol. 2.
“Kurt Russell [‘s Ego the Living Planet] in the new Guardians movie was the character that Fox swapped with Marvel to [change] Negasonic Teenage Warhead powers,” Wernick said.
In short, because Fox wanted to make substantial changes to Negasonic Teenage Warhead, they had to ask Marvel for permission, offering Ego as payment.
Guardians of the Galaxy Vol. 2 – which hits cinemas next year – received its first trailer just before the release of Doctor Strange.