Rakdos the Defiler [Ravnica Allegiance Guild Kit] Human Mercenary Knight how would I know it

how would I know it worked

Set: Archenemy: Nicol Bolas Type: Creature — Insect Rarity: Rare Cost: {G} At the beginning of your upkeep

Set: Alliances Type: Creature — Human Advisor Rarity: Uncommon Cost: {2}{W} {3}

Set: Mirrodin Besieged Type: Creature — Phyrexian Wurm Rarity: Mythic Cost: {3}{B}{B}{B} When Massacre Wurm enters the battlefield

Rakdos the Defiler [Ravnica Allegiance Guild Kit] Human Mercenary Knight how would I know itSet: Ravnica Allegiance Guild Kit Type: Legendary Creature Demon Rarity: Rare Cost: {2}{B}{B}{R}{R} Flying, trample Whenever Rakdos the Defiler attacks, sacrifice half the non Demon permanents you control, rounded up. Whenever Rakdos deals combat damage to a player, that player sacrifices half the non Demon permanents they control, rounded up.