Scrapyard Mongrel

The conditional that flips this Dog from a vanilla 3/3 into a 5/3 trampler is the entire design: control any artifact, and the body roughly doubles its threat against blockers. The clause is built to be trivially easy to satisfy in a deck that wants it, which is the point. In an artifact shell the requirement is background noise, and what you are paying four mana for is a creature that pushes damage through chump blockers rather than getting stonewalled. Outside that shell it is a beater that occasionally forgets to grow, which is the cost of pricing the artifact reward into the base rate as a static buff instead of charging mana for an activated ability. The trample rider does real work of its own: a 5/3 without it asks an opponent to find one blocker, while a 5/3 with it asks them to find five toughness or eat the overflow. It is a common-rarity payoff for an artifacts-matter aggro plan, the kind of creature whose ceiling is set by how reliably the deck around it satisfies the condition, and whose floor is a four-mana body that trades fine into the midgame even when there is no artifact in play to switch it on.