During their tenure on The Sing-Off, it was evident early on that Pentatonix were unstoppable. From overhauls of such hits as “Video Killed the Radio Star” (The Buggles) and “Dog Days Are Over” (Florence + the Machine), the group made pop music truly exciting again.

Through their fusions of explosive vocal acrobatics and polished melodies, Scott Hoying, Mitch Grassi, Kevin Olusola and Kirstin Maldonado have become platinum sellers and Grammy winners, snagging their first trophy in 2014 for their “Daft Punk” medley. They’ve released a slew of other colossal covers, EPs and one all-original studio album, 2015’s self-titled record, and they show no signs of slowing down, despite losing a member.

Earlier this year, bass vocalist and founding member Avi Kaplan departed the group. The timeline to replace him is still unknown, though. Maldonado told PopCrush recently, “Taking out one of those voices makes it difficult. We’re going to be figuring it out. We’re not trying to rush the system. Avi was super irreplaceable, and whoever we add would not be the same—but it would need to be different. We are trying to figure out what that new sound and direction is going to be.”

For now, take a stroll down memory lane with ten of the group’s best covers, below.

“Hallelujah,” A Pentatonix Christmas
Oh, boy. Excuse me, but I did have severe reservations heading into this, mostly because this is one of the most covered songs of all time. Very few artists can nail the slow crescendo or the unshakable, overwhelming urgency (forget about actually being on key) quite as well as Leonard Cohen (who released his version in 1984). But this scrappy band of vocalists come pretty close to matching the original. Trading off the lead vocals is a lovely, smart decision; each storyteller brings their incomparable style and approach to the story, making it even more universal.

“Somebody That I Used to Know,” PTX, Vol. 1
In lieu of the more alternative influence soaking Gotye’s 2011 original (from the album Making Mirrors), the band doll up their rendering with bubbly pop sensibility. The tightness of the harmony around the searing melody remains their strongest suit and is best displayed here. Only a couple months removed from the singing show, they proved they were the rightful winners, a precursor to their gradual rise to complete global domination.

“Aha!,” PTX, Vol. 1
If you’re gonna take on the one and only Imogen Heap, you better burn it completely down. Of course, this is PTX we’re talking about ⎯⎯ and they’ve set an unbelievably high bar for themselves. While remaining true to the original (from Heap’s 2009 album Ellipse), a haunting dance-club track garnished with ghoulish synths and tricky vocal effects, the outfit revamp the song with their classic splendor. Of course, Grassi on lead is genius.

“Can’t Hold Us,” PTX, Vol. 2
Macklemore is arguably a low bar to vault over, and the juggernaut group catapult ferociously over the hip-hop track, the second single from Macklemore & Ryan Lewis’ 2012 debut album, The Heist. From Olusola’s ridiculously-tight percussion and Kaplan’s rumbling bass to Grassi’s, Maldonado’s and Hoying’s galloping attacks, the anthem gets a new lease on life in the most deliciously-OTT way possible. It’s so hard not to stop from fist-pumping and belting the song at the top of your lungs, and we wouldn’t blame you one bit.

“Daft Punk,” PTX, Vol. 2
Earning the group their first-ever Grammy win, this mashup of Daft Punk hits, including “One More Time” and “Get Lucky,” not only frames their vocal talent but their arrangement capabilities. Assisted by collaborator Ben Bram, the sharp swerves between songs is breezy and intoxicating, seamlessly melting into one giant midnight rave, glitter falling hard and fast down around them. Even the added vocal distortion does not overshadow the performance. It is addicting, really.

“Mary, Did You Know?,” That’s Christmas to Me
Holiday songs can be trite without any real ounce of gusto, no matter how magical they come across. But the band turn this timeless, saccharine standard (depicting Mary’s unwitting role in Jesus’ birth) into a tour de force of relentless power, clocking 1-2 punches at nearly every turn. Their interpretation is fairly straightforward, and in true PTX fashion, the climax is oh-so gratifying.

“Jolene,” featuring Dolly Parton, PTX Vol. IV - Classics
Earning the troupe their first-ever country Grammy, for Best Country Duo/Group Performance, the reinvention of Dolly Parton’s venomous 1973 hit (from the album of the same name) is spunky, layered and brings the song into the 21st Century. Olusola’s sprightly chugs and Hoying’s enriching and expressive power belting flavor the story, and the entry is rightfully one of their career-best moments. Of course, Parton sounds as pristine as she always does, thus anchoring the moment in country tradition.

“Can’t Help Falling in Love,” PTX Vol. IV - Classics
Another song which has been done to death, especially on primetime singing shows, the group’s reworking is smooth and moving. Grassi leads, and you won’t find his classic high-flying notes here ⎯⎯ instead, he keeps things simple, sliding into his unmistakable falsetto toward the end. The King of Rock ‘n Roll named Elvis Presley, who released his original in 1961, would be tremendously proud. Ah, this is what true bliss is made of.

“Dancing on My Own”
Stripping away the electronic grit of Robyn’s original, the new version is hauntingly sparse, as Olusola strums away on his standup bass. Hoying then lends his vocal on lead, embellished with chilling harmony and injections by Maldonado and Grassi. It’s enchanting but uncomplicated. The song later builds with Olusola’s beatboxing, paying homage to the heavy dance roots.

“Problem,” PTX, Vol. III
Yeah, so: you’ll have one less problem after watching this (for the upteenth time). The band hasn’t notched their own bonafide megahit (yet), but that’s not to say they aren’t capable. Diving into one of the biggest, most bodacious smashes of 2014, by Iggy Azalea and Ariana Grande, PTX storm the R&B-tinged beats. They stick close to the original but the arrangement is something only they could have synthesized.

Pentatonix Through the Years: