Flockchaser Phantom

Convoke and the attack trigger that grants convoke fold into each other, and that loop is the entire design point. The Spirit can be cast early by tapping down a wide board, and once it swings, it hands convoke to whatever you cast next, letting your creatures pay for a second spell in the same turn without ever committing real mana to it. Vigilance closes the gap: it keeps the attacker itself available as an untapped convoke body for that follow-up cast, so you are not forced to choose between pressing damage and refueling. That interplay turns a wide board into a discount engine that compounds across a turn rather than a single cast, and the more creatures you have, the cheaper both the Phantom and everything after it becomes. The 5/5 flier is a reasonable clock, but the body is almost incidental to the machine it wants to build around itself. This is a Spirit built less to attack than to make attacking pay for the rest of your turn, a design that rewards going wide and then converting that width into tempo two spells deep.