Dragonfire Blade

The scaling equip cost is the whole design conversation here, and it points squarely at multicolored decks. On a colorless creature the equip runs the printed four mana; a monocolored body drops it to three, a two-color body to two, a three-color body to one, and a four- or five-color creature moves it for free. That gradient inverts the usual equipment math, where the equip tax is a flat toll you pay every time the equipped creature dies. Here the tax shrinks precisely in the decks whose threats are most exposed to color-based interaction, and the hexproof-from-monocolored rider tightens the fit: a gold creature wearing this blade shrugs off the mono-white exile, the mono-black targeted removal, the mono-red burn that makes up the bulk of what fair decks throw at it, while remaining answerable by multicolored spells and colorless sweepers that a rainbow deck already expects to face. The +2/+2 is deliberately modest; the payload is the protection and the cost break, not the stat line. What the card is really doing is rewarding you for the same deckbuilding choice twice, once at the color-identity level and again at the equip cost, which is a cleaner incentive than most "matters how many colors" designs manage. It is equipment built to make committing to three, four, or five colors buy you something structural rather than just fixing the mana you had to survive to cast.