Twenty years since Phish played the Beatles’s entire “White Album” as a musical costume to launch a Halloween tradition, bands — particularly in the ambitious jam-rock realm — have made offbeat covers part of the holiday routine. Perhaps that’s why Phish messed with expectations last year, surprising with a Halloween sequence of unrecorded originals that went into the Vermont band’s own upcoming album, Fuego. Many fans felt cheated, and nobody was sure whether Phish would even play a cover album this year.

Well, on a weird, ultimately wondrous Halloween that capped a week when the Allman Brothers Band played its final show, jam-bands from moe. to Widespread Panic went crazy with covers.  But Chicago’s rising Umphrey’s McGee raised the bar by unleashing wild mash-ups in its first of two nights at Boston’s House of Blues while Phish redeemed itself with a spooktacular production at the MGM Grand Garden Arena in Las Vegas.

With sleek, fearsome musicianship (plus artful lighting by ex-Bostonian Jeff Waful), Umphrey’s stands as the band most likely to ascend to the jam-band throne that Phish and fellow elders will ultimately bequeath. In past years, the sextet seemed too cleanly proficient for its own good, speaking more to the head than the heart with its technical prowess.

Thankfully, Umphrey’s has evolved into an earthier flow and nailed Halloween mash-ups both in costume (like one of Twisted Sister’s Dee Snider in a Devo hat) and music. In addition to originals that suggest Steely Dan as a prog-metal band, Umphrey’s ripped through Aerosmith’s “Sweet Emotion” and “Walk This Way,” wound with snippets of the James Gang’s “Funk #49” and even a group-wide percussion jam. The band alternated sung verses of Radiohead’s “The National Anthem” with rapped refrains of Beck’s “Loser,” plus a snatch of Phil Collins’ “In the Air Tonight.” And the group topped its Friday show with a smoking splice of the Beastie Boys’ “Sabotage” and Ted Nugent’s “Stranglehold.” It was hard to believe that Phish or anybody else could top those cover jams on this All Hallows’ Eve.

However, shortly after Umphrey’s wrapped up in Boston, Phish hit the Vegas stage for a cover-album set where the band not only made up for last year but conceptually transcended any of its previous Halloween pranks. And it was streamed for free via YouTube after technical difficulties with the first set of Phish’s paid webcast prompted the switch, a spontaneous gift that many local fans likely picked up on for a late-night treat.

Rather than a popular classic like past album choices Quadrophenia or Exile on Main St., Phish tackled an obscure sound-effects album called Chilling, Thrilling Sounds of the Haunted House. And the group bent that 1964 Disney Studios release to its own musical and theatrical whims, with holiday-appropriate set design by longtime cohort Chris McGregor.

The stage had turned into a mock graveyard of dancing zombies that echoed images from Michael Jackson’s Thriller video. A narrator from a crypt lit a fuse that sizzled across the front of a two-story haunted house where silhouettes revealed the band ferociously jamming in the upstairs windows. Then the upper walls flopped down in an explosion of lights and fog to reveal the four musicians facing each other in ghoulish makeup and white tuxedos, improvisationally rocking and riffing around the album’s spooky themes.

The spell of the Haunted House began to waver over a long set, much as with any unfamiliar dark horse. But the night included prime bookended sets of originals that also made this one of Phish’s better Halloween shows. And it was capped by an unusual encore pairing: Sudbury native Mike Gordon singing Leonard Cohen’s “Is This What You Wanted” (with its haunted house references), followed by the Edgar Winter Group’s instrumental oddity “Frankenstein,” with Page McConnell wailing away on a keytar.

Too bad Phish doesn’t stage its holiday extravaganzas closer to home these days. After two more Halloween weekend nights in Vegas, Phish (which only played one night locally this year at Mansfield’s Comcast Center) next greets 2015 with four shows in Miami, beginning New Year’s Eve. Who knows what will happen that night.