Two Sticky Bombs will down an Evie, hit your shots. If you anticipate being rushed put down a Grumpy Bomb. If you need to disengage use Poppy Bomb, then you need to finish the job before it finishes you.
Buck may try to stomp on you and scare you with his high health pool and regen. Just remember that Buck has a pitiful damage output, start on him early. If you are at or below 700 health, use an escape to regenerate. A clever Buck is deadly.
When you fight Ash as Zhin, the best thing you can do is shake her attention. Counter is generally useless against her weapon and Billow will only buy time. The best way to make Ash get off is by threatening the objective or bringing more allies.