The Tavern

Now that we finally have the Qsilver and Shadow dragon armour that we, as players, have a responsibility to extend the same privilege (of being hunted and butchered to extinction for their hides) to the two remaining true dragons in Crawl: Iron Dragons and Bone Dragons.

Obviously Bone Dragons don't have hides since they lack flesh. So instead it should be a new UNRANDART! The +5 Bone Dragon Armour - base type Shadow Dragon Armour. When you are struck by a sufficiently strong blow, a dragon skeleton falls off of you and fights for you! If it needs an additional benefit, it could grants some SH like the Ds mutation that gives bony plates.

I think once several months ago I saw this as a suggestion for Iron Dragon Armour: make it as strong as crystal plate but give it the ponderous ego.

Okay y'all I've done the exhaustive design work which, as is well known, is like 99% of the work. I leave it up to the devs to do the simple 1% of actually implementing the necessary code, art, new spawn rates, etc. Get to work you guys

It should lose some AC as it spawns the dragon.

What if, rather than some random incident that may affect the viability of the Bone Dragon Armour itself, what if it had an Evocable Ally action that instead summoned the ghostly spirit of the dragon to fight alongside you?
that way the player could control the creation of the dragon spirit, Evocations skill might be involved to the extent it works with elemental evocables, and re-use would be based on recharging in a manner identical to the elemental evocables; via XP.

TSO would also not approve use of this item.