Relentless Advance is a common Sorcery card from War of the Spark (WAR), collector number 64. Current market price: $0.12 (foil $0.37), TCGplayer market prices via Scryfall.
Amass Zombies 3. (Put three +1/+1 counters on an Army you control. It's also a Zombie. If you don't control an Army, create a 0/0 black Zombie Army creature token first.)