Heartwood Shard

The dual activation cost is the whole conceit: pay three generic mana or a single green, which makes a colorless permanent quietly partisan, happiest in a deck that can supply the discount. Run it in a mono-artifact shell and the trample tax is steep; run it in a Golgari or stompy build and it taps for one green to push a fatty past a chump blocker every combat. Trample on a stick is the most replaceable effect in Magic, printed dozens of ways across dozens of cards, so the interest is never the effect: it is the delivery. Bolting the grant to a repeatable activated ability changes the job entirely. Instead of buying a single attack step's worth of reach, the artifact stays on the table and converts every creature you cast into a threat the defender has to actually answer, turn after turn. The ceiling is genuinely narrow. Granting trample only matters when your attacker is big enough that the blocker would otherwise eat the whole hit, so the card idles in any board state where you are not the one pressing forward. It comes out of a school of cheap, colorless permanents that ask their controller to bring the payoff: the rock supplies the channel, the green deck supplies the giant that makes the channel worth opening.