The Clay dragon can be found in the basement of the Crafting Guild which require a Slayer level of 31 to kill. This dragon is the weakest dragon to drop dragon bones. It's sometimes set as a slayer task from medium and high level slayer masters. The Clay dragon seems to drop gems very often for its low combat level. It's even possible to receive an uncut onyx, but this is even rarer then getting a draconic visage from an iron dragon. The best method to kill them for lower levels is to use water spells. Higher leveled players may melee them without problems. Do not forget your Dragonbreath protection! They still breath fire hiting quite high for their combat levels. After their health reduces to 500 lp or less, you must finish them off with a bucket of water (this will empty your bucket, bu