Grumpy Bomb combined with Demolition legendary is a nightmare for Barik, especially if he's with another front liner. That's because he likes to set himself up in one place, and you are forcing him out every 10 seconds.
This is a very general tip and can work in many other cases with Seris. When you hear Drogoz ult and know he will target you (or to be safe) quickly go into shadow travel. This makes you immune to his ult and will confuse the enemy. Be fast, though!
Ruckus can activate a shield, if you are finding it hard to kill him then purchase "wrecker" from the item shop, getting it to tier 3 shreds through his shield.
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.