Maelstrom Archangel

Connect with a 5/5 flier and the biggest, most unfair thing in your hand gets cast for free. That is the whole engine, and the restrictions on it are conspicuously absent: no mana-value ceiling on what you cheat out, no "noncreature only" clause, no targeting limit. The cost line does all the balancing instead, gating the angel behind a manabase that can produce white, blue, black, red, and green simultaneously. That is the first hoop. The second is sharper: this is a combat-damage trigger, not a cast-and-win finisher, so the angel has to survive a full turn cycle and actually push through before the payoff fires. The reward lands a turn later than the cheat-the-cost crowd usually wants it, which is the real tax here, more so than the rainbow cost. Other creatures that turn an attack step into a free cast tend to cap the spell or restrict its type to keep the swing in check; this one trusts WUBRG and a connecting body to do the work, then hands you whatever you were hiding. The design wager is that anyone who can reliably assemble five colors and protect the angel for a turn has already earned the back-breaking spell they were sandbagging, so the card simply lets them have it, for nothing, the instant damage lands.