The Goblin Picaroon NM is a Goblin THF with 8-10k HP. He occasionally triple-attacks, but neither hits very hard nor evades all that much. (His accuracy does seem to increase as his HP decreases.)
If someone has killed it recently, you will receive the message "Something tells you that you should wait a moment and try again" when you click the ???.
The approximate wait time to respawn the goblin after it has been killed is 3 minutes.
Although it says requirement 1, you can do it with a party and still get credit.
Others assisting with the fight may also check the ??? after the win for an exp/limit reward regardless of whether they have the mission active. However. if they do not have the mission active, they will not receive Allied Notes or credit for the victory.