Gruul Keyrune

A mana rock has one structural flaw built into its job: it goes dead the moment your lands catch up to your color needs. This stone answers that by folding a creature into the same artifact. Tap it for red or green while you are short on fixing, then later feed both colors back in to wake it as a 3/2 trampler when the flood draws would otherwise leave you with mana and nothing to spend it on. The animation is what lifts this past inert fixing: it converts surplus mana into board pressure, and because the rock sits as a plain artifact until you commit, it ducks sorcery-speed sweepers aimed at creatures, animating only on the turn you intend to swing. The colored activation cost is the leash. You cannot turn it sideways in a deck that drifted off both its colors, which anchors it to a genuinely two-color shell rather than letting it freeload as a colorless beater anywhere. The body matches the aggressive posture exactly: a 3/2 with trample blocks poorly and does not care to, since its purpose is pushing damage past chump blockers rather than holding a line. Among its cycle-mates, this one belongs firmly in the attacking camp, a fixer that pays a second dividend on the turns its mana had nowhere better to go.