ruckus doesn't have a shield in front of him that protects from stuns, so use your reload to deal with him. just avoid his high burst damage before you stun him, after that he has to spin his weapon for a second to get it back again.
as a mal'damba you are no match for koga. try to be on lookout for him constantly watching the flank route and if you see him run away. try to get to your teammates for help slithering to the tank is a good idea if he's not busy.
it's better to focus chronos at first to get up your healing output, but when you have it at least at lvl 2, focus deft hands to help with your stuns. never go for reload speed with your cards. use your cards in a better way by focusing healing.