Covers where the lyrics are different...

[HueyRamone]

or Mustaine screwing up the lyrics to Anarchy in the UK

Mustaine didn't screw up, he intentionally replaced 70s British things like UDA, MPLA and IRA with things late 80s Americans could relate to - can't remember but wasn't it FDA, CIA and USA? Or was that n Mötley version?

Yes, he did.

He didnt know it was "I wanna destroy the passerby" and he screwed up and sang: "I wanna destroy. Possibly?"

[Anthrax442]

or Mustaine screwing up the lyrics to Anarchy in the UK

Mustaine didn't screw up, he intentionally replaced 70s British things like UDA, MPLA and IRA with things late 80s Americans could relate to - can't remember but wasn't it FDA, CIA and USA? Or was that n Mötley version?

I think that might be the Motley version. Mustaine's story supposedly is that the reason why they got the lyrics wrong is because he had misheard them, and it wasn't a conscious thing.

[NeonKnite]

Megadeth changed "These Boots" on KIMB.

From Wikipedia:

When the album started selling well, the writer of the song, Lee Hazlewood, began demanding that the song be omitted, due to its being a "perversion of the original". In the liner notes of the album's 2002 reissue, Megadeth frontman Dave Mustaine was strongly critical of Hazlewood, noting that he had received royalties for almost ten years before he objected to the altered version.[84] The song was included as a bonus track on that version, with many lyrics censored (mostly Mustaine's variations, but some other lines were also censored for comedic effect). In 2011, an uncensored live version recorded in 1987 was released as part of the 25th anniversary edition of the album Peace Sells... but Who's Buying?. In 2018, the song was released with the original Lee Hazlewood lyrics on the remixed and remastered version of Killing Is My Business... and Business Is Good![87]

In 1987, Megadeth re-recorded the song as part of the soundtrack for Penelope Spheeris' film Dudes, changing the title to "These Boots Are Made for Walkin'". This version of the song was the last song the band recorded with Gar Samuelson and Chris Poland,[88] as the two would be kicked out later in the year for their drug habits.[89] (Poland would later record with the band in 1990 and 2003–2004).

[HueyRamone]

Slayer - Now I'm Gonna Be Your God.