Oscar Isaac’s title villain in X-Men: Apocalypse was so powerful that there was really no need for the film to feature an additional villain (although it technically had four additional villains in the form of Apocalypse’s Four Horsemen followers). However, new concept art has recently been unearthed that reveals that there were initially plans to bring back a foe X-Men fans are already familiar with.
As reported by Comicbook.com, Bartol Rendulic’s X-Men: Apocalypse concept art reveals that there were plans to bring back Bollivar Trask, the villain playing by Peter Dinklage in 2014’s X-Men: Days of Future Past. Rendulic’s art features an ankle bracelet designed by Trask, suggesting that the character played a role in an early version of the film’s script.http://spinoff.comicbookresources.com/2014/02/04/bryan-singer-peter-dinklage-discuss-x-men-villains-hitler-comparisons/ Source: comicbookresources.com
When we last saw Trask, he was arrested in the aftermath of his Sentinals being compromised by Magneto (Michael Fassbender) and killing a number of people outside of the White House. In a mid-credits scene included on the Rogue Cut of Days of Future Past, Trask is shown sitting in a prison cell underneath the Pentagon, so it’s possible that the ankle bracelet concept art points to Trask being under some form of house arrest during the events of Apocalypse, which is set ten years after Days of Future Past. The most likely scenario is that Trask would have been employed by the government to help devise a way to stop Apocalypse, since Trask is something of an anti-mutant expert.
While no reason has been given for why Trask was cut from the film, it’s probably because Apocalypse already features far too many characters as it is. Admittedly, it would have been nice to see Dinklage get another crack at the character, as he was largely underutilized in Days of Future Past, but considering there are already too many subplots in X-Men: Apocalypse as it is, it’s probably for the best that he was eventually cut.