Orb of Dragonkind

Tribal payoff cards usually reward you for playing more of a type; this one instead solves the two problems that plague any deck built around expensive, color-hungry fatties. The mana ability answers the first: it fixes color and accelerates, but only into Dragons, so it never bleeds into the rest of your deck the way an unrestricted rock would. That restriction is the whole reason the rate can be this generous. Two mana of any colors from a two-mana artifact is aggressive fixing, and pinning it to a single creature type is how it pays for itself without warping formats it was never built for. The second ability answers the deck's other weakness, flooding out on lands or ramp with no threat to spend it on: sacrifice the Orb late, dig seven deep, and turn a dead accelerator into a fresh Dragon in hand. The sequencing is the point. Early, it is a mana source that only feeds your bombs; late, when the fixing has done its job, it cashes itself in for gas. It is a self-consuming engine, useful on turn two and useful again in topdeck mode, which is a rare thing for a card whose entire text box refuses to help anything but Dragons.