Angelfire Crusader

Firebreathing had been a red signature for years (Shivan Dragon and its lineage), so handing the keyword to a white body and pricing its fuel in red mana was the point of this design, not the modest +1/+0 each activation buys. The era that produced it was built to push enemy-color pairings the early game had kept apart, and a wall-shaped white Soldier that only becomes a clock once you start feeding it red mana is about as plain a statement of that intent as a common can make. The 2/3 frame is doing real work in the pitch. It survives the small-creature combat that defined the period's white decks, then converts leftover red mana into reach it would not otherwise have, pumping itself at instant speed off mana you were already holding up. As color-pie history it is a footnote, but a deliberate one: an early experiment in lending one color's iconic mechanic to another, with the red activation cost carrying the whole lesson about what kind of deck the card wants to live in.