Seize the Soul [Guildpact] Onslaught Target creature gets +1/+1 until

Target creature gets +1/+1 until end of turn for each Plains returned this way

This is Orzhov

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To understand Kaladesh

Seize the Soul [Guildpact] Onslaught Target creature gets +1/+1 untilSet: Guildpact Type: Instant Rare Cost: {2}{B}{B} Destroy target nonwhite, nonblack creature. Create a 1 1 white Spirit creature token with flying. Haunt (When this spell card is put into a graveyard after resolving, exile it haunting target creature.) When the creature Seize the Soul haunts dies, destroy target nonwhite, nonblack creature. Create a 1 1 white Spirit creature token with flying.