No, they are just there to make things a lot harder getting to your treasure.
steel or iron dragons.. there are others just these are a couple i know
I presume you was referring to the Draconic Visage. It drops from most if not all dragons. Mainly Black dragons and metal dragons most.
As I've said before there is no exact percentage on how often iron dragons drop draconic visage's but just that it is a very rare drop.
it is a rare chance to drop from metal dragons i think all but bronze
1/4500, maybe less if you are lucky.Note: Draconic Visage is listed as a "Bonus Drop!" This means that the Dragon Dropping this may also have another valuable drop such as D Legs to go with it for example!
Blue dragonhide, dragon bones, sometimes coins, etc.
There is no set number of how many times you need to kill an iron dragon to obtain a draconic visage. Some people can obtain a visage within 100 kills and a lucky few even their first however around 99% of people find trying to obtain a visage very hard as the drop rate is estimated from 1/2500 all the way to 1/15000! I myself have killed around 10,5k Dragons in total and around 1,200 of those kills being the King Black Dragon. I have failed to obtain a visage so far. Good Luck and don't give up hope!
King black dragons level one in the wilderness 47
Hmm... start killing them now, come back in about a week, then maybe you'll have one. (Ultra-rare)
Honestly there is no specific answer. My friend got one after his 3rd kill while another has killed thousands and nothing. I have heard that it is around 1/1000 though but varies as it is a random drop.
They will always drop dragon bones and green dragon hide. They also drop a variety of other items, none of which is particularly valuable - such as runes, herbs, some armour and weapons.If this is for a slayer task, you can also kill brutal green dragons instead.
There are 3 Way(s) you can get a Draconic Visage:-1st Way-Killing the King Black Dragon or a regular black dragon ( Rare Drop ).-2nd Way- ( Best )Killing the Mithril Dragon, ( Rare Drop ) also drops Dragon Full Helm ( V Rare Drop )-3rd Way- ( Easiest )Buying it off another player, either in the grand exchange, or on world 2.