You don’t choose a target for Lurking Chupacabra’s ability until after your creature has finished exploring.
2017-09-29
If a resolving spell or ability instructs a specific creature to explore but that creature has left the battlefield, the creature still explores. Effects that trigger when a creature you control explores, such as that of Lurking Chupacabra, trigger if appropriate.
Whenever a creature you control explores, target creature an opponent controls gets -2/-2 until end of turn.
