I've spent some time messing around with Seeker Zusshi's daily and I wanted to share the strategy that I found most efficient (with pets that are very easy to obtain.) I made a short (four minute) video going over the details and showing the fight, but I'll throw a summary below in case you can't watch or don't want a video.
I use a combination of snail (mine's rusty) with absorb/shell shield/dive and a Dragonbone Condor with thrash/adrenaline rush/lift-off. I find my snail absolutely thrashes any elemental ever and having the beast/flying damage moves on a single pet speeds up the fight considerably.
I also recently did a similar thing for Mo'ruk if anyone's having trouble with him. (http://www.youtube.com/watch?v=vff1OIQ3htU&)
What strategy do you use for Zusshi? Do you have a record time? (I find it fun to time the trainer dailies, makes things a little more interesting while farming them stones.)