Alyra, Frostguard Queen

When Alyra, Frostguard Queen enters the
battlefield, search your library for an instant or
sorcery card with Synergize and exile it with a
frost counter on it. Then shuffle your library.
Whenever you cast a spell for its Synergize cost
you may cast a spell from among cards you own
in exile with frost counters on it without
paying its mana cost. If you do, exile it as it
resolves with a frost counter on it.