CyberReaper

The CyberReaper was a mythical CyberMan first introduced in The Edge of Reality (video game) that seemed to phase through time, reconstructing itself out of parts of damaged and dead Cybermen. The Thirteenth Doctor believed that the purpose of the CyberReaper was simply to fight the enemies of the Cybermen, however she would later discover that it's purpose was to completely nullify the enemies of the Cybermen by sowing chaos in their timelines.