Dragonkin Berserker

Attack, then buy: the Boast structure charges you in combat exposure before it charges you in mana, and this 2/2 first striker turns that transaction into a self-fueling engine. Its own Boast pays for a 5/5 flying Dragon the first time, but because the ability that discounts Boast counts every Dragon you control (including the ones it just made), the second activation drops to , the third to , and the price curve bends downward exactly as the board that would win the game anyway grows more threatening. The first striking body is almost a footnote; its real function is to survive the swing and stay live for next turn's activation. The reduction also reaches past this card, discounting any Boast ability on any creature you control, so it bankrolls a whole suite of the mechanic once the Dragons start piling up. The catch is baked into the sequencing: you cannot activate anything without attacking first, and the discount only bites once Dragons are already on the table, so the opening activation is the full-priced one unless you already control a Dragon before the snowball takes hold. It is a payoff that rewards commitment in the most literal sense, asking you to spend the expensive turn to earn the cheap ones.