Guild Wars 2

Talking about the flame looking graphics on weapons that low level players (they are not downleveled, but actually level 2-3 etc).

How do they get those?

I think some sigils give your weapon flame effect, and you can use a lot of them at any level. It would be kinda a waste… but you “could”///

I would guess that the low level players with fire weapons would be those who earned the Hall of Monuments reward of a flame sword from their achievements in Guild Wars 1.

That would be Rurik’s sword from HoM.