Black Goblin was a short lived and relatively unknown darknet market.
It ran at Tor address
ua4aptglh45m5p6b.onionand was announced on Reddit in the DarkNetMarkets subreddit, which has since been banned due to TOS violations.
Black Goblin was launched in 2014 but it was de-anonymized shortly after.
Since the motivation behind some (most?) darknet markets was to enable illicit drug trade, being de-anonymized meant certain closure.
No user would like to be doxxed for using one of these underground marketplaces.
The de-anonymization process happened via email.
One user who has since deleted the content (and therefore we will not link to it or identify the source at their own desire to remain anonymous) explained that Black Goblin's signup process sent confirmation emails to new users.
This is, of course, a major privacy concern for secret Tor services, since email uses the open Internet.
Upon closer inspection, email headers exposed the hidden server's true IP, its Germany origin and other details.
Hackers then tested DDoS'ing the exposed IP and discovered that the hidden Tor site also went down, correlating one and the other.