If a permanent with an eerie ability enters at the same time as one or more enchantments, its ability will trigger for each of those enchantments.

An ability that triggers "whenever you fully unlock a Room" triggers when a door becomes unlocked and the other door of that Room is already unlocked, or when both doors of that Room become unlocked simultaneously.

In the unusual case where Unwilling Vessel has +1/+1 counters on it and then receives an amount of -1/-1 counters that causes it to die, use the total number of counters that were on Unwilling Vessel when it died, including all of the +1/+1 and -1/-1 counters, to determine the value of X.