The phrase "sudden appearance" refers to something or someone unexpectedly showing up or becoming visible without any warning or prior notice. Full definition
There is a general pattern in the fossil record of sudden appearance of new forms followed by «stasis» (i.e., absence of basic evolutionary change). (firstthings.com)
Fassbender plays New York businessman Brandon, a sex addict whose human contact rarely strays beyond prostitutes, internet porn and one - night stands; Carey Mulligan is Sissy, his estranged sister, a singer whose sudden appearance on Brandon's doorstep has devastating consequences for both. (theartsdesk.com)
In the annals of pitchmen, Mr. Mopar and Accy fall somewhere between Mr. Clean, whose sudden appearance in a commercial was unnerving but effective, and that inefficacious prevaricator, Joe Isuzu. (automobilemag.com)