Carnelian Orb of Dragonkind

A three-mana rock that produces the same any Signet would, priced above the two-cost artifacts because the mana carries a rider glued to one deck. Tie that to a Dragon creature spell and it hands over haste, which erases the standard tax on big flying finishers: they usually sit inert a full turn before they matter. That is the whole bargain. Outside a Dragon deck this is an overpriced rock; inside one it accelerates you into a Dragon that swings the turn it lands, folding the ramp and the summoning-sickness fix into a single artifact slot. The conditional haste is what justifies the extra mana over a cheaper rock: the mana ability is really a delivery system for a tribe-specific kicker, and the kicker only ever applies on the exact spells the deck is built to cast. It belongs to a small family of tribal mana artifacts organized around a single creature type, where the colored mana barely earns a mention and the rider is the reason the card exists. Judged on the mana alone, it would be an embarrassment anywhere that does not care what the mana touches; judged on the haste, it earns its place in the one deck that does.