Heliophial

Sunburst was the mechanic built to reward five-color manabases, and most of its recipients turned the counters into stats or efficiency. This one turns them into a Shock that scales with how greedy your fixing is: cast it off all five colors and it becomes a sacrificial five-damage bolt to any target, fired for two generic mana. The tension is that the payoff and the loading cost pull in opposite directions. The card wants you to spend wildly varied mana up front, then it sits on the battlefield as a delayed, telegraphed threat that anyone can play around once the charge counters are visible. Its ceiling is gated entirely by your willingness to run a rainbow manabase, and its floor (all-colorless mana, zero damage) is barely worth the slot. As a Sunburst design it is the cleanest statement of the mechanic's central problem: the reward is real only for decks already paying the steep cost of casting everything off every color, so the cards that want it most are the ones least able to support it consistently. The activation timing helps a little, since the damage fires at instant speed off a permanent already in play, dodging counterspells aimed at the artifact itself. But the artifact does nothing until you pay the activation, which makes the kill a two-stage commitment: five mana to deploy it, two more before it deals a point of damage.