This one is largely luck, but it helps to know how the ability works, I don't know the exact figures but it does vastly increased damage to enemies under 50% health so it is best to wait mid team fight or near when it is over and use it to pick off the stragglers. With the power of it, it is fairly easy to get so long as the circumstances are right and you have decent aim, I got lucky and managed to get it on my second play as Echo so it is not in the difficulty realms of zen's discord or lucio's wall riding achievement if anything this achievement will likely come from just standard play so long as your team is dominant.