Edit in JSFiddle

var entries = [{
  '.tag': 'folder',
  name: 'addd',
  path_lower: '/peeps/dad/addd',
  path_display: '/peeps/dad/addd',
  parent_shared_folder_id: '52130910',
  id: 'id:pt8S9nR0uAAAAAAAAAACIQ',
  client_modified: '2017-08-15T15:33:22Z',
}, {
  '.tag': 'file',
  name: 'Baywatch.2017.720p.WEB-DL.XviD.AC3-FGT.avi.et.mp4',
  path_lower: '/peeps/dad/addd/baywatch.2017.720p.web-dl.xvid.ac3-fgt.avi.et.mp4',
  path_display: '/peeps/dad/addd/Baywatch.2017.720p.WEB-DL.XviD.AC3-FGT.avi.et.mp4',
  parent_shared_folder_id: '52130910',
  id: 'id:LC0aXlQZVKEAAAAAAA9dCw',
  client_modified: '2017-08-15T15:33:22Z',
  server_modified: '2017-08-15T16:13:50Z',
  rev: '19af031b745e',
  size: 3602631401,
  content_hash: '461ac87883c6fadfd34c443f437057fc8da50f42e120c38b1b93d2fa00aef045'
}, {
  '.tag': 'file',
  name: 'Escape.From.New.York.1981.1080p.BrRip.x264.BOKUTOX.YIFY.mp4',
  path_lower: '/peeps/dad/addd/escape.from.new.york.1981.1080p.brrip.x264.bokutox.yify.mp4',
  path_display: '/peeps/dad/addd/Escape.From.New.York.1981.1080p.BrRip.x264.BOKUTOX.YIFY.mp4',
  parent_shared_folder_id: '52130910',
  id: 'id:LC0aXlQZVKEAAAAAAA9dGg',
  client_modified: '2017-08-14T19:03:14Z',
  server_modified: '2017-08-15T18:47:02Z',
  rev: '19b2031b745e',
  size: 1398858127,
  content_hash: 'f60f4b3168b653d24085e90214964e2860ee8e3ad3fa82c65702cc8d72ce5193'
}]
console.log(_.filter(entries,
  function(n) {
    //console.log(n['.tag'] === 'file')
    //console.log(['mkv', 'mp4', 'avi'].indexOf(n.name.substr(n.name.length - 3)) !== -1)
    //console.log(moment().isBefore(moment().add({days:3}).format(),'day'))
    return (n['.tag'] === 'file' && ['mkv', 'mp4', 'avi'].indexOf(n.name.substr(n.name.length - 3)) !== -1 && n.client_modified)
  }))