The mercenaries after committing 20 war crimes in less than 5 minutes:

I’m Only Humann (TF2 Mercs Edition)

Yes. That is tfc engie while the edit is for tf2 engie.

A random TF2 engineer edit i found

Original uploader: https://www.youtube.com/channel/UCG2R7rwAemWYPUaeXnuNi0A

I didn't make this song myself, but I have the original uploader's permission to reupload. Copyright goes to them! TF2 belongs to Valve!

Sappin' A River

Original uploader: 
https://www.youtube.com/channel/UCFmXN2ZE8_7qMckuM2lYZvw

TF2 belongs to Valve.

Dag Naggit Domination Overtime

Frontier Justice (Uncle Dane theme)

for those who want to listen to some rocket jump waltz and remember rick may and may he rest in peace.

Team Fortress 2 - Rocket Jump Waltz Orchestra (Extended 6 Minutes)

Precision is my game, and I've got the perfect view! Just a sniper aiming for the next big shot.

A random TF2 engineer edit i found

Virgil (classic Sniper)