Hello,
We defeated Turtle Z in Wingfril Island Beach with 2 full group this night.
The battle was very long.
First Team: 1 Tank and 3 Mages
Second Team: 4 Rangers
Average level was 13-15
He did drop Joma's pendant (soulbound item quest) and an old scroll wich contains old letter for Kulin and one mystic oil.
You can use Joma's pendant to teleport to Wingfril Temple. Becareful it's one time use.