Everyone knows the iconic metallic dragons that come in almost every single core monster book, Gold, Silver, Bronze, Copper, Brass. Let's call those the "core five"
There were some others, like dunno Steel, Iron, Platinum, Electrum, Uranium(?), and what else...
What kinds of metallic dragons other than the "core five" were shown in D&D products?
What were their ecologies and demeanors?
In what worlds did they debut/existed?
In D&D 3.5e, the most-complete listing of true dragons is in Races of the Dragon on pages 70-72. This list gives the stats of the half-dragon version of every dragon, and claims to be complete. However, the only apparent metallic dragons on the list are those from Monster Manual. Even other good-aligned dragons, namely the battle dragon, Oceanus dragon, and radiant dragon, don’t seem to be metallic. The list does mention the rust dragon from Draconomicon, which is arguably sort of metallic, but it’s notably lawful non-good.
Anyway, the Races of the Dragon list misses the steel dragon that you noted; the steel dragon was published in Dragons of Faerûn in August 2006, while Races of the Dragon was in January of the same year. Still, January 2006 covers a whole lot of the 3.5 life-cycle, so we do not have to search as many books to find other dragons. Monster Manual II and III are covered by Races of the Dragon, for instance, and Monster Manual IV has no dragons while Monster Manual V has only specific named individual dragons of existing types, not new types of dragons. Similarly, Dragon Magic focuses on magic available to and/or derived from dragons, and while it has many options for dragons, it does not have any new dragons itself.
Magic of Incarnum is semi-notorious for having a dragon, the incarnum dragon, that Races of the Dragon missed—it was published in September 2005, not long before Races of the Dragon, but nonetheless. (This is semi-notorious because its absence has been used as justification for not seeing dragonwrought kobold’s absence in the list as definitive of anything.)
So OK, every book published since September 2005, then. Using HeyICanChan’s handy list, then:
| Year | Month | Title | Checked? | Findings |
|---|---|---|---|---|
| 2005 | Sep | Magic of Incarnum | ✓ | incarnum |
| Sons of Gruumsh | ||||
| Oct | Heroes of Horror | ✓ | ||
| Magic of Eberron | ||||
| Nov | Champions of Valor | ✓ | ||
| Fantastic Location: Hellspike Prison | ||||
| Dec | Spell Compendium | ✓ | ||
| 2006 | Jan | Player's Guide to Eberron | ✓ | |
| Races of the Dragon | ✓ | |||
| Feb | Red Hand of Doom | |||
| Mar | Power of Faerûn | |||
| Tome of Magic | ✓ | |||
| Apr | Complete Psionic | ✓ | ||
| Fantastic Location: Fields of Ruin | ||||
| Voyage of the Golden Dragon | ||||
| May | Player's Handbook II | ✓ | ||
| Jun | Fiendish Codex I | ✓ | ||
| Mysteries of the Moonsea | ||||
| Jul | Fantastic Location: Dragondown Grotto | |||
| Monster Manual IV | ✓ | |||
| Secrets of Xen'drik | ✓ | |||
| Aug | Dragons of Faerûn | ✓ | mercury, mist, steel | |
| Tome of Battle | ✓ | |||
| Sep | Dragon Magic | ✓ | ||
| Faiths of Eberron | ✓ | |||
| Twilight Tomb | ||||
| Oct | Complete Mage | ✓ | ||
| Expedition to Castle Ravenloft | ✓ | |||
| Nov | Cityscape | ✓ | ||
| Dragonmarked | ✓ | |||
| Scourge of the Howling Horde | ||||
| Dec | Animated Series Handbook | |||
| Fantastic Location: The Frostfell Rift | ||||
| Fiendish Codex II | ✓ | |||
| Shattered Gates of Slaughtergarde | ||||
| 2007 | Jan | Complete Scoundrel | ✓ | |
| Feb | Barrow of the Forgotten King | |||
| Dungeonscape | ✓ | |||
| Secrets of Sarlona | ✓ | |||
| Mar | Magic Item Compendium | ✓ | ||
| Cormyr | ||||
| Apr | Eyes of the Lich Queen | |||
| Expedition to the Demonweb Pits | ||||
| Fantastic Location: City in Peril | ||||
| May | Complete Champion | ✓ | ||
| Drow of the Underdark | ✓ | |||
| Jun | Expedition to Undermountain | |||
| Forge of War | ✓ | |||
| Sinister Spire | ||||
| Jul | Monster Manual V | ✓ | dragon characters | |
| Shadowdale | ||||
| Aug | Expedition to the Ruins of Greyhawk | |||
| Sep | Exemplars of Evil | ✓ | ||
| Fortress of the Yuan-Ti | ||||
| Grand History of the Realms | ||||
| Oct | Dragons of Eberron | ✓ | dragon characters | |
| Rules Compendium | ✓ | |||
| Nov | Anauroch | |||
| Dec | Elder Evils | ✓ | ||
| 2008 | Feb | City of Stormreach | ✓ | |
| Mar | An Adventurer's Guide to Eberron |
So it seems that the mercury dragon and steel dragon were the only additional metallic dragons to ever be published by Wizards of the Coast for D&D 3.5e, both in Dragons of Faerûn. Note that web articles and/or officially-licensed-but-not-WotC-published sources like Dragon magazine are not covered (HeyICanChan notes in a comment that Dragon included adamantine, chromium, iron, nickel, sodium, and tungsten dragons). And, of course, there are many books I don’t own myself to check; none of these seems very likely to have a dragon, but there are enough of them that it seems hard to claim that none of them do.
I cannot comment on other editions, as I do not have the resources to embark on a thorough search like this for them.
& \checkmark for that book yourself.
– KRyan
Nov 21 '17 at 18:38
| ✓, which is more annoying than & \checkmark, but you are still welcome to do so (I recommend copy ‘n’ paste). Or just comment and I can do it.
– KRyan
Jan 30 '21 at 04:05