Songfacts®:

• Here, All Time Low vocalist Alex Gasgarth reflects on a toxic relationship. Though his romantic partner keeps lying to him and is making his life hell, he keeps coming back to her. The singer compares his inability to let go of the romance to monsters coming out at night.
• Gaskarth wrote the song with his frequent collaborator Andrew Goldstein ("Something's Gotta Give," "Good Times"), All Time Low guitarist Jack Barakat, and Kevin Fisher ("Life of the Party") in Palm Springs.
• The song features a verse by blackbear, who does his own take on an addictive toxic relationship. It was Andrew Goldstein, who had been working with blackbear on his new music, who suggested bringing the rapper on board. Garskarth recalled to Kerrang:
  
  "He sent back this thing to Andrew saying, 'This is kind of the headspace I'm in at the moment anyway, so I already feel like I could write something for this.' It really elevated the song."
  
  All Time Low had never dabbled in the rap realm before, so the blackbear collaboration was new territory for them.
• When the song reached the top of the Alternative Airplay chart, it became All Time Low's first-ever #1 single on any Billboard listing. It stayed at the summit for a total of 18 weeks.
• All Time Low and blackbear teamed up with friend of the band pop singer Demi Lovato for a new version of "Monster." Released on December 4, 2020, it was accompanied by a lyric video that features animated versions of Alex Gaskarth, Lovato and blackbear. The clip also shows the rest of the All Time Low members portrayed as, yep, monsters.
• The Demi Lovato remix became All Time Low's second single to chart on the Billboard Hot 100 following "Damned If I Do Ya (Damned If I Don't))," which peaked at #67 in 2009.