I'd say make a new boss monster that is part of the Giant family. It could also use 2 or 3 points of the combat triangle, or use protection prayers. And it could also drop 5-20 big bones, in lieu of dragon bones. As for location, I'd put it near goblin village(that place is pretty empty). This way, it also gives lower-levels a chance to look at it, or have something to look forward to.