Existential War

Challenge 3 (Each player reveals cards from the top
of their libraries until up to three creatures are revealed,
then put on the battlefield all creatures revealed
this way under their owners control.)
Creatures gain "Sacrifice a creature: search your library for a card, put that card in your hand then shuffle your library" until end of turn.
Untap all lands, they gain "{t}, pay 5 life: counter target spell or ability" until end of turn.
Exile Existential War.