When Flickerwisp enters the battlefield, it triggers, exiling Fiend Hunter until the next end step.
When Fiend Hunter leaves the battlefield, its second ability triggers, returning all cards exiled with it to the battlefield under their owner's control.
At the beginning of your end step, Flickerwisp triggers, returning Fiend Hunter from exile to the battlefield.
When Fiend Hunter enters the battlefield, its first ability and Preston trigger.
Resolve the Fiend Hunter trigger, exiling Flickerwisp.
Resolve the Preston trigger, creating a copy of Fiend Hunter that is a 0/1 Illusion.
When the token Fiend Hunter enters the battlefield, its first ability triggers, exiling the nontoken Fiend Hunter until the token Fiend Hunter leaves the battlefield.
When the nontoken Fiend Hunter leaves the battlefield, its second ability triggers, returning Flickerwisp from exile to the battlefield.
When Flickerwisp enters the battlefield, it and Preston trigger, with Flickerwisp targeting the Fiend Hunter token.
Resolve the Preston trigger, creating a token copy of Flickerwisp that is a 0/1 Illusion.
When the token Flickerwisp enters the battlefield, it triggers, exiling the Fiend Hunter token.
When the token Fiend Hunter leaves the battlefield, its second ability triggers, returning the nontoken Fiend Hunter from exile to the battlefield.