Martyr's Soul is a common Creature — Spirit Soldier card from Modern Horizons (MH1), collector number 19. Current market price: $0.18 (foil $0.35), TCGplayer market prices via Scryfall.
Convoke (Your creatures can help cast this spell. Each creature you tap while casting this spell pays for {1} or one mana of that creature's color.) When this creature enters, if you control no tapped lands, put two +1/+1 counters on it.