Siren's Call [Beta Edition] Explorer using their libraries as their

using their libraries as their decks

but you may put it on top of your library instead of into your graveyard

waiting for a victory only it can see

If that mana is spent on an instant or sorcery spell

then sacrifices the rest

Siren's Call [Beta Edition] Explorer using their libraries as theirSet: Beta Edition Type: Instant Rarity: Uncommon Cost: {U} Cast this spell only during an opponent's turn, before attackers are declared. Creatures the active player controls attack this turn if able. At the beginning of the next end step, destroy all non Wall creatures that player controls that didn't attack this turn. Ignore this effect for each creature the player didn't control continuously since the beginning of the turn.