When Alabaster Host Intercessor enters the battlefield, exile target creature an opponent controls until Alabaster Host Intercessor leaves the battlefield.
Plainscycling {2} ({2}, Discard this card: Search your library for a Plains card, reveal it, put it into your hand, then shuffle.)
If Alabaster Host Intercessor leaves the battlefield before its enters-the-battlefield ability resolves, the target creature won’t be exiled at all.