Karn, Silver Golem [Urza's Saga] Eldrazi Activated abilities of sources with

Activated abilities of sources with the chosen name can't be activated unless they're mana abilities

Set: The Lost Caverns of Ixalan Commander Type: Sorcery Rarity: Mythic Cost: {5}{B}{B} Destroy all creatures

where X is the number of attacking creatures

When Invasion of Segovia enters the battlefield

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Karn, Silver Golem [Urza's Saga] Eldrazi Activated abilities of sources withSet: Urza's Saga Type: Legendary Artifact Creature Golem Rarity: Rare Cost: {5} Whenever Karn, Silver Golem blocks or becomes blocked, it gets 4 +4 until end of turn. {1}: Target noncreature artifact becomes an artifact creature with power and toughness each equal to its converted mana cost until end of turn.