Blinkmoth Urn

Symmetry is the joke and the trap. The mana shows up for everyone at the start of their first main phase, scaled to artifact count, which on paper reads like a gift to the whole table. The reality is that whoever built around it sits behind a board of artifacts while everyone else banks a handful of colorless with no plan for it. This is the rare "Howling Mine for mana" design: an early-era artifact that converts a board state into a mana engine with no color commitment and no activation cost, rewarding the deck already trying to flood the battlefield with cheap permanents. The untapped clause is what gives it teeth and a wrinkle. The boost fires at each player's first main phase only if the Urn is untapped when that phase begins, which makes its tapped state a lever rather than a faucet. Because it untaps for free during your own untap step, the classic play runs in your favor: tap the Urn during your turn (sinking it into an artifact's cost, an animation, anything that uses the tap) and it stays tapped through the opponents' main phases, denying them the payout while it returns to you next turn untapped and ready. The sequencing still cuts against a careless caster, since the trigger checks on every turn and the next player in order reaches a main phase before you do. Resolved deliberately, though, the Urn is less a gift to the table than a faucet you can shut off for everyone but yourself.