Radiant, Serra Archangel

The name carries a small piece of Weatherlight-era archaeology. The original Radiant, Archangel was one of the very first legendary Angels, a 5/5 with an errata-troubled ability that grew her whenever another creature with flying entered play. This later incarnation keeps the character but rebuilds the mechanic from the ground up: instead of accumulating power off your air force, she taps your other flyers to buy protection from a color of your choice, one activation at a time. That tap cost is what makes the ability honest. Each protection grant costs you a flyer's attack or a flyer's block, so you are spending board presence to make her unkillable and unblockable against a single color for a turn, a trade you make when it matters rather than a passive shield. Protection from the color of your choice answers targeted removal, sneaks through a color-matched blocker, and walks her past combat, while the demand for a fresh untapped flyer each time stops it short of a free lock. Partner is the framing that gives all of this a home: a 6/4 flyer that turns a wide flying board into a repeatable protection engine wants a second commander to fill out the skies, and the ability rewards exactly the kind of go-wide flyers build that a two-commander shell can assemble.