Boon-Bringer Valkyrie

Backup is the mechanic that lets a creature share its whole ability suite for a turn, and this Angel is the color-pie showcase for what happens when the shared package is worth sharing. Flying, first strike, and lifelink are three of white's most conditionally-priced keywords, the sort of abilities you normally pay a premium to staple onto one body. Here they ride along on a +1/+1 counter, and the counter is the honest part of the deal: it stays, so even if the buff evaporates at end of turn, you have permanently grown a creature. Point Backup at yourself and you keep a 5/5 flier that gains life on the swing; point it at a ground attacker and that creature becomes an evasive, unblockable-in-practice threat with first strike for one combat step. The design tension is timing, not power. Backup triggers on enter, at sorcery speed by default when you cast the card, so the payoff wants a board already committed to attacking rather than a fresh topdeck. The abilities granted are exactly the ones the Angel already carries, which is what makes the effect read as coherent rather than arbitrary: this is not a grab-bag of keywords, it is a creature lending out its own identity. That coherence is the point of Backup as a mechanic, and few cards in the cycle make the loan feel as generous as a flying lifelinker willing to hand its wings to a bear.