I'll put some bangers in the comments

Tempest blitz
https://youtu.be/uG5rhaW-snI?si=NGTl-mZREDN7ly78

Battle against a true hero with lyrics (ori eta)
https://youtu.be/-pr-5GPHXzw?si=k0ERWdAt9XRkPJDw
She also made a megalovania one but I can't find it

There's also a battle against a true hero cover by Carriecore which is pretty good but I can't find it either :P

Splatter shot (big shot but splatoon) https://youtu.be/ulZkNP72JIo?si=aAy8KZh5A4BXKBNe

Super (goku vs Superman OST)
https://youtu.be/wbKDlVMd0nI?si=nrbIliGg5_fGPvRI

Will of the drill
https://youtu.be/e9g5lyj2SSs?si=A6DTf8R10Px2OTpQ

I've had enough of you
https://youtu.be/fGO1RjnprUc?si=XN2mF646HiQ2IcKL

Meteor
https://youtu.be/zQYS_9ct6-c?si=daBBCMT8PsHT2MVu

These are all really good, but for the Undertale and Deltarune ones I prefer the original

Fair enough

yeah, but these were really good