First of all, do not worry, this quest comes again several times, like 20 or sth if you want to complete everything. I used an old yellow rush deck against him (one by luuu90, like this http://i.imgur.com/yBBcx3L.png) and never lost.
Yes, that deck is really good. At the end I won also against Fungoro lev 20, and I completed the Solo mode.
Thanks to this, I got a lot of new cards (some legendary) and a lot of memoria, so I finally crafted my 3 whises deck 😀