Rage of Purphoros

Five mana for four damage to a creature is a rate that comes from a particular design instinct: charge a premium on the removal spell and staple on enough rider to soften the tempo hit. The scry 1 is doing exactly that work, smoothing the next draw on a turn you have spent your whole development killing one thing. The regeneration clause is a tell of when this kind of effect was built, an era when regenerating bodies were common enough that "can't be regenerated" earned a line of text rather than being assumed. As a creature answer it declines to compete on price: not a Lightning Bolt or a Doom Blade, but a backstop that pays a steep tax for size and offers a small consolation for the trouble. Four damage is the ceiling that defines it, enough to put down most midrange threats but blind to anything tougher, and the no-regeneration line closes the door on the recursive blockers that would otherwise shrug off straight damage. The cost keeps it out of the conversation where efficiency is the whole game, but the package (a high damage threshold, a regeneration lock, a card-selection nudge) is a coherent piece of color-pie work for red's habit of paying late and paying full freight for the privilege of putting damage on a creature.