Kalastria Nightwatch

A 4/5 for five mana is a clumsy body to build excitement around, which is exactly why the lifegain trigger has to do all the conditional work. The design bet here is that flying is worth more as a switch than as a static keyword: a creature that flies every turn is a known quantity, but one that flies only on the turns you happen to gain life forces the opponent to read your board for incidental lifegain before they block. The trigger fires on any life gain, not a specific source, which is the quiet generosity of the design: a single point from a Vampire's bite, a soul-warden effect off an Ally, any incremental tick, all of it flips the toughness-heavy body into an evasive attacker. The toughness is the tell. At 5 toughness it survives the ground stall it would otherwise create, so the card wants you to sit behind it, accrue a small life lead, and then convert that lead into damage in the air on demand. It works as a payoff for a deck already gaining life as a byproduct of its other lines; it does not earn its keep in isolation. The Ally tag points at the kind of go-wide, trigger-stacking shell where incremental life accrual is the natural rhythm of play rather than a sideline.