Belle, Scourge Valkyrie

Flying, Ward — Discard a card.
Whenever an opponent discards one or more
cards, exile one of those cards. You may look at
and play that card for as long as it remains exiled,
and you may spend mana as though it were mana
of any type to cast that spell.
{4}{b}{r}: Until end of turn, Belle gets +1/+0 for
each card discarded this turn. Activate this ability
only once each turn.