Try to place an illusion off to the side of the battlefield to teleport back to if someone, especially someone like Ruckus, starts to target you. This will work even if the illusion expires, but try to keep one hidden from the enemy at all times.
Try to stay out of his line of sight, and find where he will teleport back to so you can surprise him. Be prepared to hide quickly, because you can die very quickly to him. Try to pair up with others to minimize dmg taken and to kill him quickly.
If Skye attempts to use her ult next to you, quickly bring up your wall (impasse) to shield yourself. This might not always work, but bringing up your wall + earthen guard can make sure you survive and stay on point. Placement is key!
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!
Seris is really strong against Grover in general: just creep up behind him using your shadow travel and attack him from behind. His damage will be lower, as you will be at close range.