A lot of bands considered as "Metalcore" these days draw inspiration heavily from European melodic death metal such as In Flames and At the Gates (early 1990s).
Basically, if you were a heardcore band from Boston in the 80s and 90s, but lowkey you're a bnig fan of trash or doom or death metal, and you wanna chuck some riffs you've written into your band's music. You were a metalcore band.
Definitely more chaotic, more energetic and lots of punk sonic infleunces. The metal inflences more of the tone, strucutre and lyrical content. Instead of clean singing and or pure death growls, the bands were developing their own screaming/shouting style with callouts.
Within these 10 years the genre blew the FUCK up. Bands that sound nothing likek each other were grouped into the same genre bucket which pissed a lot of people off. There was so much variety in these 10 years I lowkey have to split it into sections.
Sounds like Melodic Death Metal with Hardcore Infleunces.
Bigger clean catchy choruses and the rise of the scene subculture widely defined this era. Personally, this is where my influences lie mostly.
Then, all the scene kids discovered they could use a laptop to make wub wubs. So, metalcore bands started to have more electornic influences. Electronicore is a term to describe bands that heavily lean into the electronic aspects. Skrillex used to be in an electronicore band called From First to Last. These bands below were really the pioneers of blending metal music, heardcore breakdowns with electronic beep boops.
Needless to say. This era was fuckin' peak.
Progressive metal meeds electronic atmosphere. And, mainstream success.
In this Erra (get it?), we get more progressive metal influences for the nerds who started off being scene kids in high school but now graduated an is an IT professional at a tech firm so they start bands like Northlane and Periphery.
Then, you get the kids who weren't super into maths, but started writing choruses and song strucutrers that mirror pop music.
When Bring Me The Horizon released Sempiternal, every band in the scene spent at least one album cycle trying to emulate what they did.
Meshuggah Rhythm + AXE-FX II atmpshere + Drop XXX tuning + Sometimes really catchy arena rock chorus
So, everyone in the Metalcore scene all collectively got together and said "We can't tell between what defines a song as metalcore and what doesnt, so fuck it we'll just mix everything"
Then there is what we define as "Revival-core". Which is pretty much any band that is making music in the 2020s that sound like Metalcore pre-Sempiternal.
Other Influences genuinely fuck with. They're sometimes clumped in with Metalcore labels, but I personally would classify them as so:
There is so much out there this just scratches the fucking surface.
Nu-metalcore: Thrown, Code Orange, Sworn In
Electronicore: A Skylit Drive, Enter Shikari, I See Stars, Electric Callboy
Deathcore: A whole 'nother rabbit hole. Just know, the scene kids who got sick of the electronic scene stuff and were into death metal and black metal decide to do invent the genre. Suicide Silence, Whitechapel, Born of Osiris, Lorna Shore.