Captain Marvel, Earth's Protector

Flash is the line that reframes everything else on this card. A five-mana 5/4 flier with lifelink is a fair body at sorcery speed; hold up the mana instead and it becomes an ambush blocker that trades up, gains life on the swing back, and dodges most sorcery-speed removal by simply not being on the battlefield when it resolves. The power-up ability is where the design shows its hand: a one-time investment that stacks a +1/+1 counter and an indestructible counter, turning her into a threat that survives board wipes and shrugs off damage-based removal. The clause that reduces that cost by her own mana cost the turn she arrives is the real engineering trick, because drops to in that window, letting you flash her in and immediately arm the indestructible counter in the same turn without paying full freight for both halves. That sequencing rewards mana that would otherwise sit unused: the flash body first, the counter second, both inside one window your opponent expected to be safe. What she asks in return is a heavy white commitment and the discipline to hold priority rather than curve her out, which is a genuinely different play pattern from the tapped-out white beaters she otherwise resembles. The counters do the work that would elsewhere require a separate protection spell, folding threat and answer into one card that only reveals its full shape when you leave the mana up.