Nex Machina

The only thing you need to look out for while going for this trophy is that you don’t accidentally run in to the boss.

Play your way through world one on rookie difficulty. When you reach 1-15, pick up a sword from the weapon crate located at the top left side. Now shoot at Beamtron to get his health to around 2-5%. Dash towards him (make sure the dash does not kill him) and use a sword attack. The sword attack will kill him granting you this trophy.