Feasting was a previous incarnation of Gluttony, some time before Craving and Gorging took up the mantle. Not much is known about Feasting. The Sins didn't seem to like it very much, presumably because it constantly tried to eat them. It had the appearance of an overlarge jellyfish/spider hybrid with tentacles coming from its huge mouth. The tentacles were used to snare prey.
Apparently, the Sins didn't take the proper time to get to know Feasting before it was elevated to Sin status, causing them plenty of trouble.