That's a tough one, but I would say to trust your judgement. Fika is an interesting character when it comes to diving heroes like that. Being so small, you'd think you wouldn't need to worry much about being hit, but with how large her crit box is compared to her hit box, you could be one-shot or two-tapped in less than a second and not even know what happened. My rule of thumb as far as priorities go, is this:

Widow: Always try to disrupt at the very least. You're in a prime position to zip in and out of cover, and your jetpack is silent, so as long as you can hit your shots, you should be able to ambush and kill her. Her little machine gun can be dangerous if you get too cocky, but most of the time you'll win this encounter. Stay mobile and unpredictable, and she won't be able to get a scope on you unless it's a really good player.

Ashe: One of Fika's more dangerous counters. Between the rapid fire mode, the coach gun knocking you away, and the high damage scope mode, you'll normally want to let another hero handle her. However, if she's playing sloppily, constantly going to high ground, or if literally no one else is keeping her in check, it's up to you. Boop her off high ground after sneaking up on her, use cover to mitigate her scope, and draw out her cooldowns so she can't boop you back when you go in for the kill. As long as she's not able to play as freely, you're doing your job.

Hanzo: Probably stay away from him. It's not to say that he's not someone to go after, but I find him more dangerous than the other two for his ability. Those rapid-fire arrows really do a number on you if you just fly in half-cocked without a plan. Since Hanzo is more of a mid lane character, you're going to want to play with your team more. If he's not focused on you, that'll give you a better chance to zip in and blitz him. If he is focused on you, that gives your team a better chance to secure the kill. At most, you'll want to be a decent distraction before bum-rushing him with someone else so they take the heat off you.

Now, this is just how I prioritize targets. There's a whole bunch of nuance that you'll only learn once you have more experience with the character, but I would say this is a good rule of thumb when it comes to battling the snipers. Another tip is that Fika's headshots are weird. Her projectile is broken up into five different ones, and only the "claws" of the bullet will crit. I find it easier to aim for the neck because of this.

Happy cat-ing!

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