Hide behind the barrier and then proceed to range or mage Rock, alternatively you can melee him and use Protect from melee prayer. He's weak against magic. He has a high range and melee defence.
The biggest and baddest troll.
Granite Shield, Shield left half, Dragon Spear
Big bones (100%), Coins (40-135), grimy herbs, noted Coal (6), Nature talisman, Nature runes, Steel platebody, Steel warhammer, Black warhammer, Mithril platebody, Uncut gems, Law runes (4), Rune warhammer, Adamant sq shield