What is a summary of the Crusade to Mahdia led by Enguerrand VII, Lord of Coucy?
As with your other question, a really good source to consult for this would be Barbara Tuchman's A Distant Mirror. It discusses this crusade at length.
This was a crusade only because the enemies were Muslim. Its whole point was not really to retake the Holy Land but instead to suppress Muslim pirates who were operating out of Tunisia and harassing Genoese and other Italian trade. The crusade was a small one, with roughly 6,000 men from France and England being transported by Genoese ships to Tunisia.
This crusade was not a complete disaster like the one to Nicopolis. However, it was no great success since it was really not well planned at all. The crusaders could not defeat the combination of a walled city (they didn't bring enough siege machines) and a relief army sent against them. They suffered due to the climate of the area. However, the Berbers were also unable to defeat them due to their heavy cavalry. This allowed the whole episode to end in something of a stalemate. The Berbers agreed to some concessions and the crusaders went away.