Only one Eldrazi stood against them, yet the defenders were outnumbered.

Flaying Tendrils

Devoid (This card has no color.)
All creatures get -2/-2 until end of turn. If a creature would die this turn, exile it instead.

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Creatures that Flaying Tendrils would cause to die will be exiled instead. The game doesn’t check to see which creatures die until after Flaying Tendrils has finished resolving.

Only creatures that are on the battlefield as Flaying Tendrils resolves will get -2/-2. However, any creature that would die that turn will be exiled, even if it wasn’t on the battlefield or wasn’t a creature as Flaying Tendrils resolved.