Squall, Gunblade Duelist

The number you name as it enters is the entire deckbuilding thesis, and it turns a Mardu build into an exercise in board homogenization. Most attack-trigger payoffs care that a creature is swinging at all; this one cares whether any attacker matches a single power or toughness value you committed to at entry, so the question stops being "how many creatures do I have" and becomes "how many of them share the number I chose." Pick one, and every mana dork, token, and utility one-drop that survives to swing contributes to the trigger. Pick a value your heavier threats share, and the same alpha strike qualifies. The lock is set at entry, but the payoff still scales forward: nothing stops later creatures from matching the chosen number, so the engine compounds with every fresh threat you cast into it. Note the trigger's exact shape: it fires once per opponent attacked, not once per attacker, so cramming ten matching one-drops into one player nets a single ping equal to Squall's power, while spreading matching attackers across three opponents fires the trigger three times, damaging each of them. That asymmetry pushes the card toward multi-front assaults rather than focused burst. The 3/2 first-striking body is beside the point; what you are building is a repeatable direct-damage tax that rewards a battlefield tuned to one number and pointed at as many defending players as your creatures can reach.